Human Inheritance Lesson 4

Transcription

1 Human Inheritance Lesson 4 May 10 6:55 PM What are some patterns of human inheritance? What are the functions of the sex chromosomes? May 10 6:56 PM 1

2 I. What are some patterns of human inheritance A. Some human traits are controlled by single genes with two alleles, and others by single genes with multiple alleles. Still other traits are controlled by many genes that act together Different traits we see are determined by a variety of inheritance patterns ex. eye color, hair color, height May 10 6:57 PM B. Single genes with two alleles A number of human trait are controlled by a single gene with two alleles ex. widow's peak, dimpled chin *single gene has either a dominant or recessive allele * these traits have distinctly different phenotypes May 10 6:59 PM 2

3 C. Single genes with multiple alleles Some human traits are controlled by a single gene that has more than two alleles *multiple alleles * three or more forms of a gene that code for that trait * Even though it is multiple alleles, a person can only carry 2 of those alleles because chromosomes exist in pairs May 10 7:02 PM * Human blood type is controlled by a gene with multiple alleles 4 main types, A, B, AB, O 3 alleles control the inheritance of blood type Type A = I A Type B = I B A and B are codominant Type AB =I A I B (expressed equally) Type O = I (recessive) May 10 7:05 PM 3

4 D. Traits controlled by many genes Some human traits show a large number of phenotypes because the traits are controlled by many genes ex. height ( at least 4 genes) skin color * Alleles of the different genes act together as a group to produce a single trait May 10 7:11 PM II. What are the functions of the sex chromosomes A. The body cells of humans contain 23 chromosome pairs or 46 chromosomes * The sex chromosomes are one of 23 pairs * The sex chromosomes carry genes that determine a person's sex as being either male or female. They also carry genes that determine other traits May 11 7:32 PM 4

5 B. Girl or Boy? The sex chromosomes are the only chromosome pair that do not always match *Girls have 2 sex chromosomes that match 2 X chromosomes * Boys have 2 sex chromosomes that do not match X and Y chromosome May 11 7:35 PM C. Sex chromosomes and fertilization When egg cells and sperm cells form, one chromosome goes with each cell * Since both female's sex chromosomes are X, all eggs carry an X chromosome * Males have 2 different chromosomes, therefore half of the male's sperm carry an X and the other half carry a Y May 11 7:38 PM 5

6 * When a sperm with an X chromosomes fertilizes an egg, fertilized egg has 2 X chromosomes = GIRL * When a sperm with a Y chromosomes fertilizes an egg, fertilized egg has an X and Y chromosome = BOY May 11 7:42 PM D. Sex linked Genes The genes for some human traits are carried on the sex chromosomes * Genes found on the X and Y are often called sex linked genes because their alleles are passed on from parent to child on sex chromosomes * These traits are called sex linked traits ex. red green colorblindness May 11 7:46 PM 6

7 a person with this trait cannot see the difference between red and green Normal vision is dominant; colorblindness is recessive *Like other genes, sex linked genes can have dominant and recessive alleles in females, a dominant allele on the X will mask the recessive allele on the other X May 11 7:49 PM in males, there is usually no matching allele on the Y to mask the X the result is any trait on the X, even recessive, will produce the trait in the male this means, males are more likely to express a sex linked trait controlled by a recessive allele May 11 7:52 PM 7

8 E. Inheritance of Colorblindness Colorblindness is a trait controlled by a recessive allele of the X chromosome * More males than females have red green colorblindness * Can see why with a Punnett square both parents have normal vision mom has a dominant for normal vision and a recessive for colorblindness (carrier) May 11 7:55 PM * Carrier is a person who has one recessive allele and one dominant allele doesn't express the recessive can pass the recessive trait onto offspring with sex linked traits, only the females are carriers because they are the ones who carry two alleles for the trait May 11 7:58 PM 8

9 Colorblindness Punnett Square Red green colorblindness is a sex linked trait. Complete the Punnett square. May 11 7:45 PM May 17 8:25 AM 9