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Chapter 12 Inheritance Patterns and Human Genetics

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1 Chapter 12 Inheritance Patterns and Human Genetics Chapter 12 Inheritance Patterns and Human Genetics

2 Objectives Tell the difference between sex chromosomes and autosomes
Define different types of mutations Evaluate and create pedigree charts

3 I. Chromosomes In the early 1990’s a researchers noticed that Drosophilia melanogaster (fruit flies) had 4 chromosomes 3 were the same in both males and females and 1 was different In the early 1990’s researchers were studying chromosomes in Drosophila melanogaster when they noticed that one pair differed in size and shape. In females the 4 pairs were of identical size and shape while in males one chromosome was shorter than the other one. Today we call them “x” and “y” chromosomes. Two X’s is a girl and an X,Y is male.

4 2 Types of Chromosomes Sex chromosomes contain genes that determine the sex of an individual (“X” or “Y”) Males decide the gender Autosomes-all the other chromosomes that are not involved in gender determination Cause about half of all genetic diseases We know that in humans girls have 2 X chromosomes and boys have an X and a Y. In other animals like chickens the males have two identical sex chromosomes while the females are the ones who have two different ones. Plants lack sex chromosomes entirely because they are asexual having both male and female parts. Sperm have a 50/50 chance of giving an X or a Y chromosome while eggs only have an X, making that the only thing they can pass on.

5 II. Linked Traits Pair of genes that are inherited together
They are located in the same chromosome and very close together. Crossing over is the exchange of pieces of DNA between homologous chromosomes.

6 Sex-linked Genes and Traits
Refers to a trait that is coded for by an allele on a sex chromosome (X or Y) More X-linked traits than Y-linked traits because the of the size difference Males who have an X chromosome that carries a recessive allele will exhibit the sex-linked trait Females have less of a chance expressing an X linked disease because they have 2 X- chromosomes Females have less of a chance expressing the trait because if they get a dominant trait and a recessive trait only the dominate trait will show. However, if the female has a son she has a 50% chance of passing along the recessive trait to him. Females can never get a Y-linked disease. Why do you think this is?

7 Mutations Germ-cell – occur in the gametes
Effect the offspring Somatic-cell – occur in an organisms body cells Can not be inherited-results in things like leukemia or skin cancer Lethal – cause death, often before birth Beneficial – help the organism survive and reproduce What is a mutation? Change in the nucleotide sequence of DNA Germ cell – don’t normally affect the individual carrying it but will be passed on to the next generation Somatic cell- a person who spends to much time suntanning might develop a mutation in a skin cell. Lethal – implies that the individual will not live long it could be months or years depending on the mutation. It can inhibit the individual from being able to perform vital functions. An example is Turners syndrome- the individual survives but is infertile so in a sense it’s lethal because their genes can not be passed on. Beneficial- pandas appear to have 5 thumbs but their thumb is actually an extension of a wrist bone. This helps them keep their grip on bamboo and gives an anvantage over other pandas who don’t have this mutation Penguins – have flightless wings and small legs not the greatest on land but masters of the water

8 Chromosome Mutations Change the structure of the chromosome
Deletion and Insertion Loss of nucleotide bases or an addition of them An example of an insertion is Huntington’s disease, the codon CAG is normally repeated times within your DNA but in people who have this it is repeated times. Normally starts when you are an adult and it is a degenerative disease in which parts of your brain waste away

9 Inversion Translocation
A piece of one chromosome breaks off and attaches to a nonhomologous chromosome A piece of the chromosome breaks off and flips around backward Homologous chromosomes occur in pairs Nonhomologous chromosomes are different

10 Nondisjunction The chromosomes don’t separate during meiosis so one gamete receives 2 copies and the other receives none.

11 2 Types of Nondisjunction
Trisomy – an extra chromosome in every cell Most of these disorders make it very difficult for the individual to survive Trisomy 21-down syndrome Trisomy 18 &13-normally die before age 1 Monosomy – absence of 1 chromosome Typically lethal to embryonic development Turner’s syndrome Trisomy is named after the chrosome which is tripled examples include Trisomy 18 & 13 have severe mental retardation and health problems involving almost every organ. Trisomy 22 is the most common cause for miscarriage. Trisomy 13 is Patau syndrome – mental retaredation, eyes may fuse together, heart defects Turner’s syndrome- affects the development of girls, they are normally short and their ovaries don’t work properly making them infertile

12 Gene Mutations Point mutation – change within a single gene
Substitution – one nucleotide replaces another Frameshift mutation – if some nucleotides are deleted the entire segment of DNA moves down changing the codons for amino acids Detrimental to the proteins function Insertion mutation – one or more nucleotides are added which can result in a frameshift mutation A frame shift mutation occurs when a deletion or substitution appear in a part of the DNA that codes for an amino acid

13 Example of Substitution
Sickle Cell Anemia: only 1 amino acid is substituted to produce the sickle shape Recessive trait that prohibits Hemoglobin from binding correctly To the red blood cell

14 Frameshift Mutation Changing one letter completely alters the codon sequence

15 Examples of gene mutations
Substitution: Original – the fat cat ate the wee rat. Mutation - The fat hat ate the wee rat. Insertion: Original: The fat cat ate the wee rat. Mutation: The fat cat xlw ate the wee rat. Frameshift: Mutation: The fat caa tet hew eer at.

16 1. Below is the base sequece for the normal protein for normal hemoglobin and sickle cell:
Normal: GGG CTT CTT TTT Sickle: GGG CAT CTT TTT Is this a point or frameshift mutation? Explain. 2. Delete the first H in the following sequence and regroup the letters in groups of three. Does the sentence still make sense? What type of mutation is this THE FAT CAT ATE THE RAT 3. Name 2 chromosome mutations. How are they alike? How are they different? 4. Using the sequence ATT GCA AAG GGT. Give an example of a deletion, insertion, and substitution. Circle the change you have made. 5. What is the difference between sex chromosomes and autosomes?

17 List of Genetic Disorders – Pick 1 for your project
Thalassemia Marfan syndrome Breast Cancer Hemophilia Cri du Chat Polydactyly Maple Syrup urine disease Turner Syndrome Klinefelter's syndrome, (XXY syndrome) Super males (XYY) Patau syndrome Albinism Huntington’s Disease Down’s Syndrome Cystic Fibrosis Duchenne muscular dystrophy Sickle Cell Anemia Trisomy 18 (Edwards) Tay-Sachs disease Color blindness PKU (Phenylketonuria) Fragile X syndrome

18 II. Pedigrees Diagram that shows how a trait is inherited over several generations

19 Reading Pedigrees A square represents a male
A circle represents a female A square represents a male If the circle or square is filled in that means the individual has the trait Horizontal lines indicate marriage or having children Vertical lines show offspring

20 Practice Problems Is the mom or dad in generation I affected by a trait? How many offspring are shown in generation II? How many daughters & sons in generation II? How many have the trait? How many offspring does daughter #1 have?

21 Patterns of Inheritance
Autosomal Dominant Traits Passed on to sons or daughters even if only one parent has the gene Affected individuals who mate with an unaffected individual have a 50% chance of passing on the gene as long as they are not homozygous for the trait Can appear in males and females equally

22 What is the genotype of #9?
What must the genotype of the parents be to produce a child #7 who is unaffected? What is the genotype of #9? What are the genotypes of the 3 children in the third generation? #7 = heterozygous #9 – heterzygous Third generation – homozygous recessive

23 Recessive Pedigrees In order to be passed on both parents must have the gene Traits can be passed on if both parents are “carriers” of the trait Have the trait but it isn’t expressed because they also have the dominant trait An individual who is infected may have parents who are not If both parents are affected, all of their children will be affected

24 Carriers for Autosomal recessive traits
We know this trait is recessive because neither parent expresses it but they have a child who has it. This makes them both carries of the allele because they both passed the recessive allele down. The other child got at least one of the dominant alleles from the parents but we can’t tell whether he is homozygous dominant for the trait or recessive.

25 Recessive Pedigree If individuals in generation 3 have more children- will they be affected? Can Individual #8 in gen. 3 have any unaffected children? Can individual #9 in gen 3 have affected children? All children of individuals 2 and 3 will be affected #8 can only have unaffected children if they mate with someone who has a dominant allele #9 yes because we can’t tell if they are homozygous for the trait or a carrier

26 Sex Linked Traits Located only the sex chromosomes (X and Y)
More frequently expressed on males than females Y-linked is male only X-linked –passed from mother to son Mainly expressed in males Daughters are carriers

27 X-linked Traits Traits that are on the X chromosome
Males are affected more than females Color blindness is an X-linked recessive disorder passed from mother to son Color blindness is an x-linked recessive disorder, women carry the gene but do not express it because they have 2 copies of the X chromosome. Pass it on to their sons because they get only 1 X chromosome. normal vision see this as 29, red/green see it as a 70. Those with normal vision will see this as a 5 and those who are color blind will read it incorrectly or not at all Normal is 15 color blindness is 17

28 X-linked recessive Evident in males because they only have 1 X chromosome Women are rarely affected because they have 2 X chromosomes-better chance of not getting it If the father has the mutated gene all of his daughters will have it If males get the mutant gene then they will have the trait. Girls will be carriers unless the mother is a carrier and the father has the disease Example is duschenne muscular distrophy

29 X-linked Dominant No transmission from father to son
All daughters of the affected male will have it Only 1 dominant allele is needed for the trait to be expressed What is the genotype of #2 in generation II?

30 Genetic Disorders Diseases that have a genetic basis
Researchers have found that most traits are Polygenic – influenced by several genes Skin color – combination of 3-6 genes which control the amount of melanin in the skin Complex characters – influenced by both genes and environment Height, certain diseases such as breast cancer Breast cancer can run in families, but environmental factors include a diet high in saturated fat

31 Incomplete Dominance Displaying a trait that is intermediate of the two parents Wavy hair comes from one parent having straight hair and one parent having curly hair Red flower and a white flower produce a pink flower

32 Sex Influenced Trait Males and females can show different phenotypes even when they share the same genotype Ex: Male pattern baldness – the allele is dominant in males but recessive in females due to the higher testosterone levels in males

33 Single-Allele Traits Trait controlled by 1 allele-dominant or recessive Recessive Examples Cystic Fibrosis-most common lethal disease Sickle-cell anemia-blood disorder Albinism- lack of color pigment in skin, hair, and eyes Dominant Examples Huntington’s Disease- degradation of the brain Polydactly- presence of a sixth digit Achondroplastic dwarfism-dwarf size

34 Detecting Genetic disease
Amniocentesis – technique used to detect genetic disorders in a fetus Chrionic villi sampling – takes some cells derived from the placenta Treatments depend on the specific disease The do this by removing some of the amniotic fluid from the sac that surrounds the fetus between the 14th and 16th week of pregnancy. This allows them to look at the chromosomes and proteins in the fluid. Carries a slight risk of miscarriage. Sample taken between the 8th -10th week

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