The Human Genome Chapter 14

The Human Genome – Chapter 14 Biology 122

Section 14-1: 1. Why do cell biologists photograph chromosomes during mitosis when making karyotypes?

The chromosomes are fully condense and easy to see

2. How do you distinguish between male and females on karyotypes?

Males are XY and Females are XX (sex chromosomes)

3. What is a pedigree chart?

A chart with shows the genotype/phenotype relationships within a family

4. How are the following things represented in a pedigree? (a) females circles (b) males squares (c) marriage horizontal line connecting a male and female (d) children of parents a vertical line and a bracket connecting parents and children (e) a person not affected by the gene a circle or square that is not shaded

5. Human traits are almost impossible to associate with single genes. What are the two reasons for this?

First things you might think of as single traits such as the shape of your eyes and ears are actually polygenic, meaning they are controlled by many genes Secondly, many of your personal traits are only partly determined by genetics. They are also affect by environmental factors such as nutritional and exercise

6. Do the problem solving activity on page 343 Albinism is recessive. Both sets of grandparents are carriers (heterozygous) The father is affected and the mother is a carrier because she passes the trait onto one son and one daughter (They are albino so they are homozygous recessive and have received one allele for mom and one allele from dad) All their offspring are carriers because the father is albino (homozygous recessive and only have recessives alleles to give his offspring)

7. What is the human genome? When was it published? Our complete set of genetic information. 2003

8. (a) What are the two best known traits that determine human blood type? The ABO blood groups and the Rh blood groups

(b) What are the genotypes for Rh positive? Rh+Rh+ or Rh+Rh-

(c) Why would an AB blood type be fatal if used for a blood transfusion of a Type A patient? Type AB blood has both antigens produced and type A have only A antigens. The B antigens would attach the Type A persons blood cells

(d)If a woman with type O blood and a man with type AB blood have children, what are the children’s possible genotypes?

2/4 AO and 2/4 BO

9. Explain what happens with the recessive disorder PKU and cystic fibrosis.

See chart page 345

10. What are two examples of genetic disorders caused be dominant alleles? Why are these disorders more prominent in society?

Dwarfism and Huntington disease. Dominant alleles have a higher percentage of occurrences because they have two genotypes –homozygous dominant or heterozygous dominant.

Section 14-2 1. The average human gene contains how many base pairs? The largest human gene?

3000 base pairs. 2 million base pairs

2. What are sex-linked genes? Genes carried on the X or Y chromosome

3. What is the only gene carried on the Y chromosome? Testis-determining factor

4. Explain again why red-green colorblindness occurs 1 in 10 for males and 1 in 100 for females. This trait is carried on the X chromosome and is recessive. Males only have one X chromosome and there for do not have a back-up plan, a second X that may overshadow the recessive trait with it dominant allele.

5. Name two other sec-linked genes and give a sentence describing both. Hemophilia - blood clotting problems and Duchenne Muscular Dystrophy – progressive weakening and loss of skeletal muscle

6. Females have two X chromosomes, but males have only one. If just one X chromosome is enough for the cells in males, how does the cell “adjust” to the extra X chromosome in female cells?

In female cells, one X chromosome is randomly switched off. This turned off X chromosome forms a dense region in the nucleus known as a BARR BODY

7. Why is Mary Lions important? First to discover BARR BODIES 8. Why are cats that are white with orange and black spots almost always female? In all mammals, one of the X chromosomes is turned off in a cell. In cats one X codes for orange spots and one codes for black spots. Male cats only have one X so they have orange or black spots. Female cats have both X’s and some code for orange spots and some for black depending on which X is turned off in that particular cell.

9. End of the Chapter Questions: Questions 23,25,29 page 364 Questions 1-7 page 365 (multiple choice)

10. A recessive sex-linked gene (b) located on the X chromosome increases blood-clotting time. This causes the genetic disease, hemophilia. (a) Explain how a hemophilic offspring can be born to two normal parents. Mom is a carrier (b) Can any of the female offspring develop hemophilia? No because Dad is always passing on his healthy X