1. Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch
Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch. 26: Inheritance of Traits & Ch. 27: Human Genetics

2. Genetics & Heredity What is genetics? The study of heredity
passing of traits from parents to offspring
Genetics is the study of heredity Heredity the passing of traits from parents to offspring

3. Chromosomes in Cells Remember… Body cells are diploid
2 of each chromosome
1 from mom & 1 from dad
Gametes (sperm & eggs) are haploid
1 of each chromosome
Why?
Why? So that when fertilization occurs the zygote has the correct # of chromosomes… if gametes were diploid then the zygote would have double the correct # of chromosomes

4. Genes Why is your combination of genes unique?
Chance… don’t know which sperm will fertilize which egg
get ½ of your chromosomes from mom & ½ from dad
Meiosis
crossing over during prophase 1
“independent assortment” of chromosomes based on alignment during metaphase 1
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.

5. Genes & Alleles What is a gene?
section of chromosome that determines a specific trait (ex. hair color, eye color, ear shape, etc.)
genes are paired on homologous chromosomes
different forms of genes for the same trait are called “alleles”
Organisms have thousands of different traits.
Each chromosome has different kinds of genes that control different traits…
Remember… chromosomes in body cells are paired (homologous)… so, the genes on chromosomes are paired too….
Different forms of genes for the same trait are called alleles

6. Dominant & Recessive Alleles
Each parent contributes 1 allele (form of gene) for trait
Can be:
dominant
prevents expression of (“masks”/“hides”) recessive trait
recessive
seen only when pure (homozygous) for trait
Represented with letters
usually first letter of dominant trait
same letter used for dominant & recessive
CAPITAL = dominant
lowercase = recessive
Different forms of genes for the same trait are called alleles
Dominant  “speaks for both alleles”
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype (2 copies of recessive allele)
Use same letter to represent dominant & recessive… dominant shown by CAPITAL & recessive shown by lowercase

7. Allele Combinations If both alleles are: the same different
homozygous (pure) dominant (ex. AA)
homozygous (pure) recessive (ex. aa)
different
heterozygous (hybrid) (ex. Aa)
Different forms of genes for the same trait are called alleles
Homozygous  inherited two identical forms (or alleles) of the gene
can be homozygous dominant
can be homozygous recessive… This is the ONLY way for the recessive trait to be expressed
Heterozygous  inherited two different forms (or alleles) of the gene
dominant allele is always expressed; recessive allele is “hidden” by dominant allele

8. Genotype vs. Phenotype
genotype = actual genetic make-up of individual (alleles)
codes for phenotype (trait)
represented by 2 letters
represent alleles from mom & dad
ex. PP, Pp, pp
phenotype = outward (physical) expression of the genotype
trait we “see”
(due to) the protein that is produced
usually represented by an adjective
ex. purple, white, etc.
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
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

9. Genotype is Expressed as a Phenotype
Ex. Let P = purple & p = white
homozygous (pure) dominant
genotype PP
phenotype = purple
heterozygous (hybrid)
genotype Pp
dominant trait “masks/hides” recessive trait
homozygous (pure) recessive
genotype pp
phenotype = white
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
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

10. genotype = actual genetic make-up of individual (alleles)
genotype = actual genetic make-up of individual (alleles) codes for phenotype (trait) represented by 2 letters
1 to represent gene from mom & 1 from dad ex. PP, Pp, pp
phenotype = outward (physical) expression of the genotype trait we “see” (due to) the protein that is produced
usually represented by an adjective ex. purple, white, etc.
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

11. Predicting Traits in Offspring
Punnett Squares
Help predict the results of crosses (mating)
Letters along top & side represent possible alleles in gametes of each parent
Boxes represent possible allele combinations (genotypes & resulting phenotypes) in offspring
Can be used to determine probability and ratios
1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes
5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring)
Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt
Phenotypes: 50% tall & 50% short

12. Making a Punnett Square
Parents are Tt & tt genotypes…
So… Tt x tt is our cross
1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes
5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring)
Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt
Phenotypes: 50% tall & 50% short

13. Passing Traits to Offspring & 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?
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 boys is (1/2)^4, or 1/16
Five girls? (1/2)^5, or 1/32

14. Passing Traits to Offspring & Ratios
genotypic ratio = probable ratio of genotypes in offspring of a cross
Ex. If cross Pp & Pp
1PP : 2Pp : 1 pp
phenotypic ratio = probable ratio of phenotypes resulting from the genotypic ratio
3 purple : 1 white
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.

15. Passing Traits to Offspring & Ratios
expected ratio = ratio expected based on probability (Punnett Square)
observed ratio = 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.

16. Passing Traits to Offspring
If one parent is homozygous dominant & other is homozygous recessive
each parent can only produce gametes with 1 type of allele
All offspring will always have:
heterozygous (hybrid) genotype
ex. Ss or Pp
dominant phenotype
ex. smooth or purple
Monohybrid cross = If one parent is homozygous dominant & other is homozygous recessive

17. Passing Traits to Offspring
If both parents are heterozygous
each parent can produce gametes with 2 types of alleles
Offspring will always have:
1 homozygous dominant : heterozygous : 1 homozygous recessive genotype ratio
ex. 1 SS : 2 Ss : 1 ss
3 dominant phenotype : recessive phenotype ratio
ex. 3 smooth : 1 wrinkled

18. What are the genotypic ratios & phenotypic ratios of each generation?
Phenotype
genotype
p P
P p Pp Pp Pp
Phenotype
genotype Pp
What are the genotypic ratios & phenotypic ratios of each generation?
Parents = homozygous purple (PP) x homozygous white (pp)
First generation offspring = all heterozygous (Pp) purple offpsring
Second generation offspring =
genotypic ratio = 1 PP (homozygous dominant purple) : 2 Pp (heterozygous purple) : 1 pp (homozygous recessive white)
phenotypic ratio = 3 purple : 1 white

19. Gregor Mendel – the Father of Genetics 1822-1884
Austrian monk did his work around 1865….

20. Mendel’s Experiments Studied garden pea plants
7 different traits with clearly different forms
Tried to determine how these traits were passed from parent to offspring
Used peas b/c reproduce much more quickly and could use many plants at once

21. Mendel’s Experiments
Mated pure purple parent (PP) & pure white parent (pp)
All offspring had:
purple phenotype
heterozygous (hybrid) genotype Pp
Noticed purple flowered-plants mated with white-flowered plants always resulted in purple-flowered offspring

22. Mendel’s Experiments
Heterozygous (hybrid) offspring allowed to self- pollinate
So… Pp x Pp
New offspring weren’t all purple
all F1 plants should have Pp (if cross pure purple w/ pure white)…. All first generation offspring plants should produce ½ their gametes w/ P gene & ½ w/ p gene… so 3 possible combinations for 2nd generation offspring…. PP, Pp (x2), and pp 3:1 phenotypic ratio expected & observed….

23. Mendel’s Principle of Dominance
Mendel noted that one form dominates over the other
dominant trait prevents the expression of the recessive trait
Ex. In peas, purple x white gives all purple offspring
PUPRLE = dominant
white = recessive
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.
Principle 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

24. Dominant/Recessive is Not Always the Mode of Inheritance
Traits are not always as clearly defined as the 7 pea plant traits Mendel studied
Examples of non-dominant/recessive inheritance
Sex determination
Sex-linked traits
Codominance
Multiple alleles
Called non-Mendelian modes of inheritance

25. Sex Determination humans have 46 chromosomes (in body cells)
23 pairs
Pairs 1 – 22 = autosomes (body chromosomes)
23rd pair determines gender = sex chromosomes
XX = female
XY = male
Which parent’s chromosomes determines if the offspring will be a boy or girl????
Why?
What is the probability of having a son?
A daughter?
Which parent’s chromosomes determines if the offspring will be a boy or girl???? Father b/c mother always contributes X chromosome… if dad contributes X  girl… if dad contributes Y chromosome  son
So…. Blame dad if you didn’t get the little brother/sister you wanted….

26. Sex-linked Inheritance
X & Y chromosomes not fully homologous
X is bigger & carries more genes
Males will have only 1 allele for traits carried only on X
called X-linked or sex-linked
Ex.:
In Drosophila (fruit flies) eye color
In humans  hemophilia & colorblindness
X-linked traits & disorders are more common in males
Why???
X-linked traits & disorders more common in males Why??? 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 is a group of bleeding disorders in which it takes a long time for the blood to clot.

27. Sex-linked Inheritance
Predictions made using Punnett square
Consider the sex chromosomes (X or Y) & genes they carry (shown as superscript/exponent) together as a unit…
ex. XG (= dominant gene), Xg (= recessive gene), Y (= no gene)
If a female is heterozygous,
she does not show the
trait/have the disorder,
but is a carrier
can pass gene
to offspring
XG female Xg
XG XG XG Xg
XG Y Xg Y XG
Male Y

28. Sex-linked Inheritance
Ex. In Drosophila (fruit flies)  eye color
What are the sex, genotype, & phenotype of each offspring?
Are there any female carriers for the white eye gene?
Make sure students know symbols for male & female… Male… arrows… hunting… female… arms… gathering (or hugging)
What are the sex, genotype, & phenotype of each offspring?
Top picture  2 females with XRXr red eyes (carrier for white eye gene) 2 males with XrY white eyes
Bottom picture  Female XRXR red eyes Female XRXr red eyes (carrier for white eye gene) Male XRY red eyes Male XrY white eyes

29. Codominance heterozygote (hybrid) shows both traits
shown by 2 different capital letters
Ex. Roan cow
phenotype = mix of both red & white hairs
genotype = RW
heterozygote displays the protein products of both alleles equally
Shown as 2 different capital letters.
Roan (RW) cattle are the heterozygous hybrids of a cross between a white bull (WW) and a red cow (RR).

30. Multiple Alleles more than 2 different forms of an allele exist
but individual still has just 2
Ex. human blood types
exhibits multiple alleles (3)
IA (A)
IB (B)
i (o)
also exhibits codominance
IA = IB (A & B are codominant)
i (o is recessive)
So… (IA = IB) > i
How many possible genotypes are there?
How many phenotypes?
Can you spot the blood type that is the result of codominance?
How many possible genotypes are there? (AA, AO, BB, BO, AB, O)
How many phenotypes? 4 (A, B, AB, O)
Can you spot the blood type that is a product of codominance? AB
rules for assigning symbols to alleles demand that all three be represented by some version of the same symbol. In this case, that common symbol is the letter "I," which stands for "immunoglobin."

31. Human Genetic Disorders

32. Human Genetic Disorders
Due to DNA mutation (usually recessive) or chromosome abnormalities (in # or structure)
Causes production of abnormal proteins
Examples:
Autosomal recessive disorders (***most genetic disorders)
Cystic Fibrosis
Sickle-cell Anemia
Tay-Sachs Disease
Autosomal dominant disorders
Huntington’s Disease
Sex-linked disorders
Hemophilia
Color Blindness
Chromosomal abnormality disorders
Down Syndrome (trisomy 21)
Klinefelter’s Syndrome (XXY)

33. Autosomal Recessive Disorders
To be affected, must be homozygous b/c allele is recessive
Cystic Fibrosis
Sickle-cell Anemia
Tay-Sachs Disease
in all of these examples
Do the parents have the disease? No (both ARE carriers)
If they only had one child, what would the chance be for that child to be affected by the disease? ¼ or 25%
What is the probability that the child would be a carrier? 2/4 or ½ or 50%

34. Autosomal Dominant Disorders
To be affected, can be homozygous or heterozygous b/c allele is dominant
Huntington’s Disease

35. Sex-linked Disorders Hemophilia Color blindness
Left pic hemophilia: Mother carrier & father affected with 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
Right pic colorblindness: 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

36. Sex-linked Disorders 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?
Left pic: 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
Right pic: 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

37. Sex-linked Disorders Colorblindness is X-linked recessive
In this Punnett square, what are the genotypes & phenotypes of the parents?
Ishihara
test for
red-
green
color
blindness
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.
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.

38. Chromosomal Abnormalities in Number
abnormal number of chromosomes:
Caused by non-disjunction
failure of paired chromosomes to separate during meiosis 1 or meiosis 2

39. Chromosomal Abnormality Disorders
Down Syndrome (trisomy 21)
person has 3 copies of chromosome # 21
Caused by non-disjunction
3 copies of chromosome # 21

40. Chromosomal Abnormality Disorders
Klinefelter’s Syndrome
Sex chromosome disorder
Males have extra copy of X chromosome
XXY (or 47, XXY b/c 47 total chromosomes)
caused by non-disjunction
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's syndrome is typically caused by what is called non-disjunction. If a pair of sex chromosomes fails to separate during the formation of an egg (or sperm), this is referred to as non-disjunction. 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.

41. Chromosomal Abnormalities in Structure
abnormal structure of chromosomes:
added, deleted, inverted, or translocated pieces

42. Detecting Abnormalities
karyotyping
“picture of human chromosomes”
From blood sample
Can detect extra chromosomes or chromosomal abnormalities

43. Detecting Abnormalities
Amniocentesis
sample of fluid surrounding fetus
can detect Down Syndrome
Chorionic villus biopsy
sample of cells from chorion
Amniocentesis 14th + week of preg.
sample of fluid surrounding fetus (karyotype then made); use ultrasound to help make sure don’t harm fetus
Can detect Down Syndrome
Chorionic villus biopsy 9th + week of preg.
sample of cells from chorion (part of structure by which fetus linked to mother)

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