Unit 6: Genetics & Heredity Ch 8: Heredity & Ch 11: Human Genetics

Unit 6: Genetics & Heredity Ch 8: Heredity & Ch 11: Human Genetics
What is genetics? __________________ = the passing of traits from parents to offspring Why is your combination of genes unique? Genetics is the study of heredity Heredity the passing of traits from parents to offspring Why is your combination of genes/traits unique? ½ your genes (on chromosomes) came from your mom, ½ from your dad! But – you also have your own unique gene combination! b/c when the egg and sperm that became your first cell were formed during meiosis, crossing over & independent assortment mixed up your genes, giving you a one-of-a-kind genotype…unless you are an identical twin! This genetic recombination, all based on chance, is what gives all living things variation, and this is what drives the process of evolution.

Gregor Mendel – the Father of Genetics 1822-1884

Mendel’s Experiments Studied garden peas – _____ different traits with clearly different forms Tried to determine how these traits were transmitted from parent to offspring

Male & female parts in same flower
Mendel’s Experiments Male & female parts in same flower Normally Self pollinate Produce pure offspring ______ parents produce______ offspring ______ parents produce _________ offspring Mendel noticed that pea plant flowers can be purple or white, and that flowers are the sex organs of plants. He took pollen (male gametes) from purebred purple flowers, and transferred it to the female structure of purebred white flowers. These two plants, purple (WW) and white (ww) made up the P, or parental generation. The W signifies the dominant, or purple-coding allele, while the w signifies the recessive, or white-coding allele.

Mendel’s Experiments Cross pollination of pure purple parent & pure white parent (parent generation) Purple offspring (________ ____________ generation) Hybrids (genes for both purple & white in all offspring)

Mendel’s Experiments Offspring allowed to self pollinate
New offspring (F2, second filial, generation) weren’t all purple _______ Parent Pure parental plants each had 2 identical genes for a trait… Mendel reasoned that the 2 genes segregate during gamete formation… so sperm/egg would have just 2 gene for each trait… all F1 plants should have Ww (if cross pure purple w/ pure white)…. All F1 plants should produce ½ their gametes w/ W gene & ½ w/ w gene… so 3 possible combinations for F2 generation…. WW, Ww (x2), and ww 3:1 phenotypic ratio expected & observed…. First filial Crossed 2 F1 plants to get F2 Second Filial

Mendel’s Principle of Dominance
Mendel noted that for each trait one form dominates the other In other words, the __________ trait prevents the expression of the _______________ trait. Ex. In peas, purple x white gives all purple offspring ____________________ The Law of Dominance/Recessiveness Genes (Mendel called them “factors) come in pairs – one from the egg and one from the sperm. Each gene of a pair is called an allele. An allele may be either dominant, which means only one copy of the allele is needed in the organism’s genotype for its protein product to be expressed in the phenotype, or it may be recessive, in which case two copies of the allele need to be present in the genotype for its protein product to be expressed in the phenotype. Law of dominance When an organism has two different alleles for a trait, the allele that is expressed, overshadowing the expression of the other allele,is said to be dominant. The gene whose expression is overshadowed is said to be recessive Mendel then cross-pollinated two purple pea plants (Ww) from the F1 generation, and got a big surprise! Their offspring, called the F2 generation (second filial), appeared in a ratio of 3 purple-flowered plants to 1 white-flowered plant. What do you think their genotypes were?

Punnett Squares Helps to predict the results of crosses
all possible resulting offspring & the probability of each offspring’s genes Ea. parent can contribute 1 of 2 genes for a trait (______)- found on homologous chromosomes Represent with letters ________________ = dominant gene ________________ = recessive gene ________________ – alleles same ex. AA or aa ________________ – alleles different ex. Aa Homozygous: When an organism contains 2 identical alleles for a trait Homozygous dominant: 2 dominant alleles, e.g., PP Homozygous recessive: 2 recessive alleles, e.g., pp Heterozygous: When an organism contains 2 different alleles for a trait (1 dominant and 1 recessive), e.g., Pp Monohybrid cross: Between 2 parents with different forms of 1 trait Dihybrid cross: Between 2 parents with different forms of 2 traits

R & r and T & T are alleles R & T are not

Genotype vs. Phenotype ____________________ = actual genetic make-up of individual represented by letters __________ = outward (physical) expression of the genotype (due to) the protein that is produced Ex. Let P = purple & p = white Genotypes PP & Pp both have the same phenotype (purple) PP = ________________ dominant Pp = ________________________ Genotype pp has (white) phenotype: pp = ________________ recessive Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles Two alleles/genes/letters for each trait Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles

Mendel’s Principle of Segregation
During gamete formation, the pair of genes responsible for each trait separates so that each gamete receives only 1 gene for each trait. happens during meiosis I when homologous chromosomes line up equator (metaphase 1) & separate (anaphase 1) Draw diagrams Genes (alleles) segregate (separate) during gamete formation When does this occur? During metaphase 1 of meiosis Chromosomes come in pairs, called homologous chromosomes. Each chromosome is called a homolog Homologous chromosomes carry information (genes) for the same traits, but their information may be different (alleles may be dominant or recessive).

Genes for different traits segregate (separate) independently of each other during gamete formation When does this occur? During metaphase 1 of meiosis Homologous chromosomes, carrying gene pairs (alleles), may line up at the equator in different ways during metaphase 1. This allows for genetic recombination, or variation, which is the fuel of evolution! Where else does genetic recombination occur during meiosis? During prophase 1 – crossing over!

Draw Punnett Square tested segregation using heterozygous purple flower & homozygous white flower Predicted _______ purple & ____ white offspring b/c: P gene would combine w/ p gene _______ the time producing __________ _____________ flowers p gene would combine w/ p gene _______ the time producing ___________ _____________ flowers According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance.

Mendel’s Principle of Independent Assortment
Genes for different traits segregate independently during gamete formation when they are located on different chromosomes… What if they are on the same chromosome? If they are on the same pair of homologous chromosomes, they are said to be “linked” and DO NOT sort independently Genes on same chromosome meiosis Genes on same chromosome

Probability The chance an event will occur
What is the chance of getting heads? Tails? If you flip two coins, of getting 2 heads? tails? What is the chance of a couple having a boy? A girl? Of having four boys? Five girls? Draw Punnett Square If you flip two coins, of getting 2 heads? ½ x ½ =1/ tails? ½ x ½ =1/4 What is the chance of a couple having a boy? ½ x ½ =1/ A girl? ½ x ½ =1/4 Of having four boys? The probability of having a boy is 1/2. The probability of having 4 girls is (1/2)^4, or 1/16 Five girls? (1/2)^5, or 1/32

Ratios _________________________= probable ratio of genotypes in offspring of a cross Ex. If cross PP & pp 1PP : 2Pp : 1 pp _________________________= probable ratio of phenotypes resulting from the genotypic ratio 3 purple : 1 white ________________________________ = ratio expected based on probability (Punnett Square) ___________________ = what actually occurs Why would these be different? Expected & observed ratio can differ b/c it is possible (although less probable) that 4 offspring with the same traits…. The larger the # of offspring, the more likely the 2 ratios will be closer… The phenotype ratio in a monohybrid cross is never exactly 3:1. This is because of the random nature of fertilization and the fact that some embryos die during early stages.

Phenotype genotype p P P p Pp Pp Pp Phenotype genotype Pp

Monohybrid Cross a cross where __________________________ ________________________ (gene) is studied ex. only height, flower color, eye color, etc... Draw Punnett Square T t A monohybrid cross is a cross where only one characteristic, i.e. one gene, is studied e.g. only height or only flower color, eye color etc... In an experimental monohybrid cross, the parents are true-breeding. (Organisms which has two identical alleles for a gene, in other words, it is homozygous for this gene). However, they are chosen so that each has a different phenotype for the characteristic studied.

Dihybrid Cross involves study of inheritance patterns for organisms differing in _______ (ea. w/ 2 forms). Mendel  determine if different traits of pea plants, such as flower color & seed shape, were inherited independently. Both parents originally had this genotype: (Ee, Tt). The parents are known as “dihybrids” because they each have 2 hybrid genes. When dihybrids make gametes, they produce 4 possibilities which are listed on top and on the side of the box below. Dihybrid Cross Animation

Dihybrid Cross 2 traits with 2 forms
Supports hypothesis of independent assortment b/c if dependent (YR & yr always together) would not get as varied results Would get 3:1 ratio as in a monohybrid cross with heterozygous parents….

Test Cross Used to determine __________________ of dominant phenotype
Cross ______________ phenotype w/ ________ phenotype If any offspring show recessive trait, unknown parent  ____________ If all show dominant trait, then parent  ________ ____________________ Show as P_ Test cross: An organism with a dominant phenotype may either be homozygous dominant, or heterozygous. If the genotype is unknown, the organism is crossed with a homozygous recessive organism. If the offspring all show the dominant phenotype, then the parent is homozygous dominant. If half the offspring show the dominant trait, and half show the recessive trait, then the parent is heterozygous. Why would a dog breeder need to know this? Draw Punnett Squares

Dominant/Recessive is Not Always the Mode of Inheritance
Traits are not always as clearly defined as the 7 pea plant traits Mendel studied Incomplete dominance Codominance Multiple alleles Sex-linked inheritance Polygenic inheritance Continuous variation

Incomplete Dominance No allele is ________ __________________
results in _ phenotypes – ________________, ___________ (mixed), __________________. Genotypic & phenotypic ratios same ___________________ Ex. Pink four o’clock flowers Draw Punnett Square

Codominance heterozygote displays the protein products of both alleles __________ Ex. Roan cow has a mixture of both red & white hairs. Roan cattle are the heterozygous hybrids of a cross between a white bull and a red cow.

Multiple Alleles More than _______________ different forms of an allele exist, but individual still has just 2. Ex. alleles that code for human blood types A = _____ B = _____ O = _____ exhibit both codominance & multiple alleles (______= ______ ) > ______ Copy Chart How many possible genotypes are there? How many phenotypes? Can you spot the blood type that is a product of codominance? AB How many possible genotypes are there? How many phenotypes? Can you spot the blood type that is a product of codominance?

antigen antigen antigens No antigens
An antigen is a substance, usually a protein or a glycoprotein, which, when injected into a human (or other organism) that does not have the antigen, will cause an antibody to be produced. Antibodies are a specific type of immune-system proteins known as immunoglobulins, whose role is to fight infections by binding themselves to antigens. In the case of the ABO blood groups, the antigens are present on the surface of the red blood cell, while the antibodies are in the serum. These antibodies are unique to the ABO system and are termed "naturally occurring antibodies." The table shows the relationships between blood types and antibodies. antigen antigens No antigens

Multiple Alleles Agouti rabbits 4 alleles: C, cch, ch, c
w/ dominance relationship to one another: _________________________________ agouti rabbit (wild type) Phenotype: brown, Genotype: CC, Ccch, Cch, or Cc “Chinchilla” (mutant) Phenotype: silvery gray, Genotype: cchcch, cchch, or cchc “Himalayan” (mutant): Phenotype: white w/ black points, Genotype: cchcch chch or chc “Albino” (mutant) Phenotype: white, Genotype: cchcch cc

Sex Determination In humans chromosomes:
Pairs 1 – 22 = ____________________ 23rd pair determine gender = __________________ __________ = female __________= male Draw Punnett Square What is the probability of having a son? A daughter?

Sex-linked Inheritance
X & Y chromosomes not fully homologous X is bigger & carries more genes Males will have _____________________ for traits carried only on X called _______________________________ Ex.: In Drosophila (fruit flies) eye color In humans  _______________________________ ___________________________________________ X-linked traits more common in males Why??? X & Y chromosomes not fully homologous X is bigger & carries more genes names not based on shape, merely means of identification X-linked traits/disorders more common in males b/c female has XX, more likely she will have a copy of dominant allele… males XY… can only get dominant allele on X Hemophilia refers to a group of bleeding disorders in which it takes a long time for the blood to clot.

Predictions made using Punnett square Include sex of each parent Consider the sex chromosomes & genes they carry together as a unit… ex. XG (= dominant gene), Xg (= recessive gene), Y (= no gene) XG female Xg XG Male Y Complete Punnett Square

Ex. In Drosophila (fruit flies)  eye color What are the sex, genotype, & phenotype of each F2 offspring? Are there any female carriers for the white eye gene? Heterozygous red-eyed carrier for white eye allele P generation genotypes were XRXR & XwY Make sure students know symbols for male & female… Male… arrows… hunting… female… arms… gathering (or hugging) What are the sex, genotype, & phenotype of each F2 offspring? Female XRXR red eyes Female XRXw red eyes (carrier for white eye gene) Male XRY red eyes Male XwY white eyes red-eyed

Hemophilia is X-linked recessive If mother is carrier & father has hemophilia: genotypic ratio? phenotypic ratio? If mother is carrier & father is normal: Make a Punnett square genotypic ratio? phenotypic ratio? Mother carrier & father hemophilia Genotypic ratio 1 XhX : 1 XhXh : 1 XY : 1 XhY Phenotypic ratio: 1 female carrier : 1 female hemophiliac : 1 normal male : 1 hemophiliac male Mother carrier & father normal Genotypic ratio 1 XX : 1 XXh : 1 XY : 1 XhY Phenotypic ratio: 1 normal female : 1 female carrier : 1 normal male : 1 hemophiliac male Draw Punnett Square

pedigree chart showing inheritance of hemophilia Does hemophilia affect one gender more often? Why?

Colorblindness is X-linked recessive In this Punnett square, what are the genotypes & phenotypes of the parents? Father: genotype = XCY phenotype = colorblind mother: genotype = XCXc phenotype = carrier for color blindness Color blindness is the inability to see certain colors in the usual way. Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light-sensitive layer of tissue at the back of the inner eye. If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too. Ishihara test for red- green color blindness

Polygenic Inheritance
______________ ______________ affect a single trait shows range of phenotypes from one extreme to another (_______ ______________) Ex. in humans: hair color, height, skin color

Expression of Genes Genes can _______________________ to control various other patterns of inheritance Most characteristics that make up individual’s phenotype not inherited in Mendelian patterns Ex. Modifier genes affect eye color influence amount, intensity, & distribution of melanin (color pigment) in eye cells

Expression of Genes ____________________________ in which organism develops is another factor that affects expression Probably due to how enzymes (proteins) operate at different temperature Higher temps may “deactivate” enzyme & prevent a reaction form occurring (therefore, changing phenotype) Examples: temp & size of fruit fly wings: Warmer temps = larger wings & colder temps = smaller wings __________: Low altitudes = taller & high altitudes = shorter ____: Poor soil or drought may produce shorter (or no) ears _______ seedlings: Green (dominant) & albino (recessive)… however green color is also affected by environment No sunlight green color cannot be expressed due to lack of chlorophyll production Put in light green will appear b/c chlorophyll being produced Green is a dominant trait to albino in tobacco leaves. The parents of the tobacco seeds used in this experiment were both heterozygous for green/albino. Therefore, an expected ratio of 3:1 (green: albino) is predicted. A ratio of approximately 3:1 will result when the seedlings are grown in the light environment. In the dark, however, the genotype cannot express itself due to the lack of light necessary for chlorophyll production. The seedlings will all look albino when grown in the dark. When placed in the light (after being in the dark), the phenotype will quickly change to green in those seedlings possessing the gene for green. This should restore the predicted 3:1 ratio.

Human Genetic Disorders

Pedigree Charts A ____________________________ ______________________________ of family over several generations Scientist or a genetic counselor would find out about your family history & make this chart to analyze. used to find out probability of a child having a disorder in a particular family To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive. A pedigree is a chart of the genetic history of family over several generations. Scientists or a genetic counselor would find out about your family history and make this chart to analyze it. For example, a couple might like to know their chances of having a child that has muscular dystrophy. So the scientists or a genetic counselor would find out who had muscular dystrophy in the mother’s and/or father’s families. This information would be used to and then calculate the probability of the couple having a child with MD.

Pedigree Chart Square = ___________________________
Circle = ____________________________ Shaded = __________________________ Marriage = _________________________ Offspring = _________________________

Human Genetic Disorders
Due to DNA mutation (usually recessive) or chromosome abnormalities (# or structure) Causes production of abnormal proteins Examples: ______________________________ (***most genetic disorders) Cystic Fibrosis Sickle-cell Anemia Tay-Sachs Disease _________________________________________________________ Huntington’s Disease _____________________________________________________ Hemophilia Color Blindness Down Syndrome (trisomy 21) Klinefelter’s Syndrome

Autosomal Recessive Must be _____________ b/c allele needed to produce trait is _______ Cystic Fibrosis Sickle-cell Anemia (A normal, S sickle-cell trait) Tay-Sachs Disease Complete Punnett Squares Do the parents in this example have the disease? If they only had one child, what would the chance be for that child to be affected by the disease? What is the probability that the child would be a carrier? A female S A Male S

Autosomal Dominant Can be homozygous or heterozygous b/c allele needed to produce trait is dominant Huntington’s Disease Draw Punnett Square

Sex-linked Disorders Hemophilia Color blindness
Complete Punnett Squares Mother carrier & father hemophilia Genotypic ratio 1 XhX : 1 XhXh : 1 XY : 1 XhY Phenotypic ratio: 1 female carrier : 1 female hemophiliac : 1 normal male : 1 hemophiliac male Mother carrier & father normal Genotypic ratio 1 XX : 1 XXh : 1 XY : 1 XhY Phenotypic ratio: 1 normal female : 1 female carrier : 1 normal male : 1 hemophiliac male

Chromosomal Abnormalities
Affects ________ ____________ of chromosomes #: Down Syndrome (____________ … _______ copies of chromosome # __) Cause  _______ ______________ (failure of paired chromosomes to ______________ during meiosis 1 or meiosis 2) 3 copies of chromosome # 21

Detecting Abnormalities
Klinefelter’s Syndrome Sex chromosome disorder Males have ________ __________________ _______ chromosome *XXY (or 47, XXY b/c 47 total chromosomes) Cause  __________ __________________ (failure of paired chromosomes to __________________ during meiosis 1 or meiosis 2) Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans. About one of every 500 males has an extra X chromosome, but many don’t have any symptoms. Klinefelter syndrome is typically caused by what is called nondisjunction. If a pair of sex chromosomes fails to separate during the formation of an egg (or sperm), this is referred to as nondisjunction. When that egg unites with a normal sperm to form an embryo, that embryo may end up with three copies of the sex chromosomes (XXY) instead of the normal two (XY). The extra chromosome is then copied in every cell of the baby's body.

Chromosomal Abnormalities
Affects # or structure of chromosomes Structure: Added, deleted, inverted, or translocated pieces

______________ “picture of human chromosomes” From blood sample Can detect _____ ______________ ______________ ______________ ______________ (additions, deletions, inversions, translocations)

_________________ sample of fluid surrounding fetus (karyotype then made) Can detect _________ __________________ 14th + week of preg. _________________ _____ sample of cells from chorion (part of structure by which fetus linked to mother) 9th + week of preg. For amniocentesis use ultrasound to help make sure don’t harm fetus

Review & Animations Vocab interactive Crosses Drag & drop genetics
Crosses Drag & drop genetics Various Pedigrees Genetic disorders

Unit 6: Genetics & Heredity Ch 8: Heredity & Ch 11: Human Genetics

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Unit 6: Genetics & Heredity Ch 8: Heredity & Ch 11: Human Genetics

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