Quarter 3 HSA Review Session Genetics, Punnett Squares and Pedigrees

genetics

What is genetics? The study of heredity, which is the passing of genetic traits from parents to offspring. Gene and environment determine characteristics- may have height and build similar to parents, but env. factors such as nutrition and exercise can affect traits. Plants- env. Factors such as water, fertilizer, sunlight, etc. affect traits. Simase cat- dark color at areas with low temps. Extermities- tail, nose, ears, paws. Shave belly but cold pack on it will grow back black.

Genetics Vocabulary Vocabulary Term Definition Dominant Recessive Homozygous Heterozygous Genotype Phenotype The allele that is expressed The allele that is hidden or masked when a dominant allele is present When the 2 alleles of a particular gene in an individual are the same (ex: PP and pp) Make this the cut and paste activity slide When the 2 alleles of a particular gene in an individual are different (ex: Pp) An organism’s genetic makeup; set of alleles (ex: PP, Pp, pp) The physical appearance of a trait (ex: purple flowers or white flowers)

Punnett squares

Punnett Square A punnett square is a tool that can used to predict the results of a genetic cross Can be used to predict the probability of passing on autosomal or sex-linked traits to offspring Parent 1 One allele One allele One allele Parent 2 One allele

Autosomal vs. Sex-Linked Traits The majority of traits that we inherit from our parents are not dependent on our sex → autosomal traits. Genetic traits such as tongue rolling and having a widow’s peak will appear equally in both sexes. However, certain traits are dependent upon one’s sex. They are determined by genes that are found on the sex chromosomes → sex-linked traits. Example: Hemophilia (X-linked recessive disorder)

Autosomal Punnett Square Problem Tall is dominant in pea plants, and short is recessive. T=tall and t=short. What are the genotypic and phenotypic ratios for a cross of a homozygous tall plant with a heterozygous tall plant?

Homozygous tall x Heterozygous tall TT TT t Tt Tt Genotypic ratio- 1 TT : 1 Tt Phenotypic ratio- 1 tall: 0

Sex-linked Punnett Square Problem Hemophilia is an X-linked recessive disorder. A woman has hemophilia. She marries a man, who also has hemophilia. Write the genotypic and phenotypic ratios.

Xh Xh XhXh XhY Xh Xh Xh Y Genotypic ratio- 1 Xh Xh: 1 XhY Phenotypic ratio- 1 female with hemophilia: 1 male with hemophilia

Genetics and punnett square questions

Question 1 Which of these combinations results in the expression of a recessive trait? two dominant alleles a dominant sex-linked allele and a Y chromosome two recessive alleles a dominant allele and a recessive allele

Question 2 Which of these is an example of a heterozygous genotype? Rr wrinkled round

Question 3 In humans the trait of having freckles (F) is dominant to not having freckles (f).Which genotype and phenotype are correctly paired? FF—no freckles Ff—no freckles Ff—freckles ff—freckles

Question 4 One kind of chromosomal mutation can occur during meiosis when a pair of chromosomes that carry genes for the same trait fail to separate. Which of these represents the sex chromosomes of a male organism when this type of chromosomal mutation has occurred? XXY XX XY XXX

Question 5 Red-green color blindness affects about 7.0% of the human male population. It affects approximately 0.4% of the human female population. These data suggest that red-green color blindness is a dominant trait carried on the Y chromosome dominant trait carried on the X chromosome recessive trait carried on the Y chromosome recessive trait carried on the X chromosome

Question 6 In humans, the allele for dimples (D) is dominant. The allele for not having dimples (d) is recessive. A woman (DD) and a man (Dd) have four children. Which of these is the predicted ratio of the children with dimples to the children without dimples? 1:0 1:1 1:3 3:1

Pedigrees

What is a pedigree? A diagram that shows the occurrence of a genetic trait in several generations of a family Indicates a Mating Indicates offspring Normal male Normal Female Affected Male Affected Female Carrier (Female)

Interpreting a Pedigree 1. Determine if the pedigree is autosomal or sex-linked If the disorder occurs equally amongst men and women the disorder is autosomal. If most of the males in the pedigree are affected by the disorder, it is sex-linked

Interpreting a Pedigree Determine whether the disorder is dominant or recessive If the disorder is dominant, only one parent of the affected child must have the disorder. If the disorder is recessive, neither parent of the affected child has to have the disorder because they can be heterozygous. The second step is to determine if the disorder is dominant or recessive. It is important to find out if a disorder is dominant or recessive. For example, Huntington’s disease is a dominant disorder. If you have only one dominant gene you will have Huntington’s disease, which is a lethal disorder. The disorder does not show up until a person is in their middle ages such as 45. It will quickly decrease their motor skills and the brain will begin to deteriorate. If a disorder is dominant, one parent must have the disorder (either homozygous dominant (TT) or heterozygous recessive (Tt). Both parents do not have to have the disorder. One parent might not have the disorder or be a carrier. If a disease is dominant, it does not skip a generation unless one parent is heterozygous dominant (Tt) and the other parent is homozygous recessive (tt). In this case the child has a chance of not receiving the dominant gene. If the disorder is recessive, a parent does not have to have the disorder, but could still pass it to their offspring. This would happen when a parent is heterozygous recessive (Tt) and passes on the recessive (t) gene. This means this disorder can skip generations. An example of a recessive disorder would be sickle cell anemia. 22

The pedigree above traces the inheritance of dimples in a family. Is the pedigree autosomal or sex-linked? Is it dominant or recessive? Label the genotypes of all of the individuals in the pedigree.

The pedigree above traces the inheritance of colorblindess in a family. Is the pedigree autosomal or sex-linked? Is it dominant or recessive? Label the genotypes of all of the individuals in the pedigree.

Pedigree questions

Question 7 In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2. Which of these individuals in the pedigree is a male with the genotype aa? Individual I-1 Individual II-2 Individual III-2 Individual III-5

Question 8 Individuals III-6 and III-7 have two In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2. Individuals III-6 and III-7 have two children and are expecting a third child. Their two children have flat feet. What is the chance that the third child will have normal arches? 25% 50% 75% 100%

Question 9 the cross between Individual II-4 and Individual II-5? In humans, the allele for having feet with normal arches is dominant (A). The allele for flat feet is recessive (a). The pedigree below shows the occurrence of normal arches and flat feet in four generations of a family. In the pedigree, individuals are identified by the generation and Individual numbers. For example, Individual 2 in Generation I is identified as I-2. Which of these Punnett squares shows the cross between Individual II-4 and Individual II-5?