Extending Mendelian Genetics (Chapter 7)

Genetics is never Simple Mendel studied traits that were autosomal and were either-or traits. We find that very few traits are controlled by one gene or that an allele is either dominant or recessive.

A

C

I. Gender Determination Gender = the sex of an organism Female vs. Male All humans have 46 c’somes, 23 came from your mother’s egg, and 23 came from your father’s sperm. The 23rd pair of chromosomes determine whether you will be female or male.

Karyotype of male human’s 23 pairs of chromosomes

1. Females Females = organisms with 2 “X” chromosomes. All eggs thus contain only one “X” chromosome to donate to their offspring.

2. Males Males = organisms with 1 “X” and 1 “Y” chromosome. Sperm contain EITHER one “X” chromosome OR one “Y” chromosome to donate to their offspring.

II. Offspring Gender Again, the mother can ONLY donate an X chromosome to offspring… The father can donate EITHER an X or a Y, so the gender of the offspring is determined by the FATHER!!! If a sperm with a Y is used, the child is male. If a sperm with an X is used, the child is female.

Gender Punnett Squares X X X XX XX XY XY Y

B

III. Sex-Linked Traits Sex-Linked Traits = traits that are inherited on the sex chromosomes. The X chromosome is capable of holding many more genes than the Y chromosome. For this reason, more sex-linked disorders are found in men then women. WHY????

A. Recessive Disorders Most sex-linked disorders (like hemophilia and colorblindness) are recessive. Women have 2 X chromosomes, which means they would have to inherit two recessive genes. Men only have 1 X chromosome, which means if they inherit a recessive gene from their mother, they will HAVE the disorder!

Women can be CARRIERS of a disorder and not even know it. Men CANNOT be carriers: men either have the disorder or do not. c X X Carrier of colorblindness c X X X X X c Y X Y X Y Colorblind!!!

IV. Sex-Linked Disorders Colorblindness The inability to see or distinguish between certain colors. The two most common forms are “red-green” and “blue-yellow” colorblindness.

B. Hemophilia A condition in which the blood does not clot properly. Can lead to bleeding to death from a simple scrape or bruise. Common in royalty due to inbreeding.

Again…

Common Sex-Linked Traits or Disorders Hemophilia Color Blindness Baldness

C

V.Pedigrees A PEDIGREE is a chart for tracing genes in a family. Human pedigrees: Boxes= males Circles= females Shaded= person shows a certain trait Unshaded= person doesn’t show a certain trait Half Shaded= carrier of a trait

Pedigrees You can use a pedigree chart to predict genotypes by looking at the phenotypes recorded. If roughly the same amount of males and females show a certain phenotype then you are tracing an autosomal trait If there are more males that show a certain trait, you are tracing a sex linked trait.

Karyotypes A KARYOTYPE is a picture of all of the chromosomes in a cell. Chemicals are used to stain the chromosomes which makes bands appear so that genes can be located and identified. Klinefelter Syndrome

Example of Trait = Albinism Pedigree Charts Show relationships within a family In genetics: Used to show how an inherited trait is passed through a family Example of Trait = Albinism

Symbols Circle = female Square = male Normal or without trait = unshaded Trait = shaded

Symbols If an individual has one recessive allele for a trait, the person is a carrier. This is shown with a half-shaded square or circle.

Symbols Married couple or couple producing offspring = horizontal line connecting midpoint of circle and square

Symbols One offspring Multiple Offspring How do you differentiate between a brother and sister and a husband and wife on a pedigree? Multiple Offspring

Generations Each generation is (often) labeled with a Roman numeral. Oldest generation at top of pedigree Current generation at bottom

Generations Individuals in each generation may be numbered or named. 1 2 1 2 3 4 5 6 1 2 3 4 5 Individuals in each generation may be numbered or named. Siblings are placed in birth order from left to right.

Analysis How many offspring were produced by generation 1? Number of boys? Girls? How many of generation 11 were married with children? Deaths are shown with a slash. 1 2 1 2 3 4 5 6 1 2 3 4 5

Polydactyl Trait Who is the first individual with the trait on the pedigree chart? Who did individual #7 generation III inherit the trait from?

Polydactyl Trait Based on the pedigree chart, is the trait for multiple digits (fingers and toes) dominant or recessive? How can you tell?

Analysis of a Recessive Trait How many individuals on this pedigree have the trait? How many are carriers?

HINT: Dominant Traits NEVER skip a generation Analyzing a Trait HINT: Dominant Traits NEVER skip a generation Sometimes a pedigree is drawn without the carriers shown. Can you tell if the trait is recessive or dominant? Explain.

Dominant or Recessive Trait?

Dominant or Recessive Trait?

VI. Complex Inheritance Incomplete Dominance= neither allele is completely dominant nor completely recessive. - Heterozygous phenotype is intermediate between the two homozygous phenotypes - Homozygous parental phenotypes not seen in F1 offspring

B. Codominant alleles= both be completely expressed. - Codominant alleles are neither dominant not recessive. - the ABO blood types result from codominant alleles. Both incomplete dominance and codominance yield a 3 phenotype not seen before. (always your hybrid).

Traits that are expressed by more than one gene are called polygenic traits. Human skin color = 4 genes Human eye color = 3 genes Fur color = 5 genes

Polygenic traits

C. Linked Genes= genes that appear to be inherited together (like red hair and freckles). - They are not inherited together every time. - Remember, homologous c’somes exchange genes during meiosis. - The closer together two genes are, the more likely they will be inherited together.

C. The environment interacts with genotype and can affect phenotype: - the sex of sea turtles/ gators depends on both genes and the temperature of the environment. (hot = male (91+) cool = female (86) - Size of some animals are determined by the space available.