Human Genetics Chapter 7 1

The Role of Chromosomes A. Chromosome number 1.Each human sperm/egg has 23 chromosomes 2.Each human body cell has 23 pairs of chromosomes 3.Each type of organism has a different number of chromosomes. Humans - 46 chromosomes Fly – 8 chromosomes Cat – 38 chromosomes PAIRS

The Role of Chromosomes Chromosome number - The last pair of chromosomes, or the 23 rd pair are called the sex chromosomes. - Males have an X and a Y chromosome (XY) - Females have two X chromosomes (XX) - Autosomes do not determine a person’s gender. They are body chromosomes. They determine ones characteristics! - Chromosome #1-22 3

X & Y Chromosomes & Traits X chromosome much larger than the Y 4

Amniocentesis, a sampling of the fetal fluid which then can help determine if there are any genetic disorders of the developing fetus. Geneticist will look at the chromosomes of the fetus. A way to tell chromosome number Karyotype

Human Traits A. Incomplete dominance, neither allele/gene is completely dominant nor completely recessive. - Heterozygous phenotype is in between the two homozygous phenotypes - individual is a blend Snap dragons (flowers) RR= Red ww= White If a red snap dragon were crossed with white snapdragon, the heterozygous plant would be PINK! RR x ww Offspring = Rw = pink 6

B.Codominance - Codominant alleles/genes are both fully and separately expressed. - Both phenotypes are shown in the Heterozygous individual. - Black hamster crossed with a white hamster - BB X WW - The heterozygous individual BW, would be both black and white in color. 7 B B W W BW

Co-dominance and Multiple Alleles in Blood Types Example: Blood Types The four blood types are Type A, Type B, Type AB, Type O 8

The 3 multiple alleles are A, B, and O A and B are always dominant to O. –AO = A type blood –BO = B type blood

A and B are NOT dominant to each other, they are Codominant So remember… There are 3 alleles (A, B, O), however there are 4 blood types. (A, B, AB, O)

GenesBlood type OOO type ABAB type AA or AOA type BB or BOB type Cross a woman Heterozygous for A-blood and a man with AB-blood –Parent genotypes: –Genotypes: –Phenotypes: A O A B AA BO AO AB 11 AO x AB 1AA:1AB:1AO:1BO 1: AB type 2: A-type 1: B-type

More Codominance Sickled Red Blood Cell African American Population Resistance to Malaria Normal Red Blood Cell

Sickle Cell NN= Normal Blood Cells SS= Sickled Blood Cells NS = Both Normal and Sickled Cells Cross a heterozygous mom with a heterozygous dad for blood cells. 13 Parent genotypes: Genotypes: Phenotypes:

NOW YOU TRY: Bb x Bb as Complete, Incomplete, & Co- Dominance Say that: B = Black b = White W = White Complete Dominance Incomplete Dominance Co-Dominance Genotype Ratio Phenotype Ratio 1BB: 2Bb: 1bb 1BB: 2Bb: 1bb 1BB: 2BW: 1WW 3 Black : 1 White 1 Black : 2 Gray : 1 White 1 Black: 2 Black & White: 1 White

Polygenic Traits Polygenic traits are produced by two or more genes. This occurs when many genes interact to produce one trait. Example: Eye Color, skin color, height 15

C. Sex-linked traits - Genes on the X chromosome 1. Only the X Chromosome carries genes so if a gene is on the X chromosome, the female would have TWO of those genes and the male would have only ONE. XY XX Female that has the disorder Female carrier for a disorder Male that has the disorder

C.Sex-linked traits -A genetic disorder that is found or linked to the X chromosome ONLY -Females can carry a sex-linked genetic disorder and not have the disorder. -This is known as being a carrier of the disorder. -In order for the female to have the disorder both X chromosomes must have the gene for the disorder -Males (XY) express all of their sex linked genes because they only have one X chromosome. -If the X chromosome has the gene, the male has the disorder. -Males can not be carriers because they only have one X chromosome -Examples: Hemophilia and Colorblindness 17

X Y XX 1. Colorblindness a sex-linked recessive trait. (C- normal vision; c- colorblindness) In order for a female to be color blind, she would have to have two colorblind genes. A male needs to only have one colorblind gene.

Colorblindness - is a sex-linked recessive trait. (C- normal vision; c- colorblindness) In order for a female to be color blind, she would have to have this many colorblind genes. _______ A male needs to have this many _______ It is more likely to have a colorblind male than a colorblind female because ______________________________________ The male only needs one gene

What do you see?

A woman is heterozygous for Normal vision. She marries a man who is colorblind. What is the predicted colorblindness outcome for their children? LET … N = normal vision and n = color blind Parent genotypes: X N X n x X n Y Mom Dad FIND THE: Genotypic Ratio: Phenotypic Ratio: X N XnXn XnXn Y

Answer: LET … N = normal vision and n = color blind MOM = heterozygous normal vision. X N X n DAD = colorblind. X n Y X N XnXn XnXn Y XN YXN Y X n XN XnXN Xn Xn YXn Y Genotypic Ratio 1X N X n : 1X n X n : 1 X N Y : 1 X n Y Phenotypic Ratio 1 normal female carrier : 1 colorblind female : 1 Normal male : 1 colorblind male 22

X Chromosome Inactivation Males and females can differ in sex linked traits. –The expression of genes on the sex chromosomes differs from the expression of autosomal genes. –Genes located on the sex chromosomes are called sex- linked genes or X-linked genes. –Males express all of the alleles on both sex chromosomes. –In females one of the two X chromosomes is randomly turned off by a process called X chromosome inactivation. 23

Environment + Genes Your phenotype is not just dependent on your genes, but also the environment Examples –Sea turtles gender –determined by the temp of sand –Gender of alligators – determined by temp. –Height of people- influenced by nutrition 24

A pedigree is a chart for tracing genes in a family. Phenotypes are used to infer genotypes on a pedigree. Autosomal genes show different patterns on a pedigree than sex-linked genes.

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