Chapter 12

Patterns of Heredity and Human Genetics

Chapter 12.1 Scientific Terms

1. Pedigree2. Carrier3. Fetus

1. What is a pedigree? How do you make one?

Pedigree graphic representation of genetic inheritance- looks like a “family tree”

It is made of a set of symbols that identify:- male or female- the trait being studied- the relationships between the members

2. Describe how you would analyze a pedigree. Why are these useful?

Pedigrees show “carriers”, which are heterozygous individuals

You can follow a trait through generations by looking at a pedigree

Helpful for knowing the possibility of genetic disorders, or any recessive trait

3. Describe what “simple recessive heredity” refers to. Describe the three recessive disorders that the book discusses.

Genetic disorders caused by a homozygous recessive situation (rr or tt, etc)

1. Cystic fibrosis 1 in 28 white Americans carry the recessive allele (Rr)- 1 in 2500 white kids born with it

2. Tay-Sachs common in Amish people and Jewish people from eastern Europe

3. Phenylketonuria common in descendants of Norway and Sweden

4. Describe what “simple dominant heredity” refers to. Overview the several dominant traits that the book discusses.

A trait is inherited with at least one dominant allele (RR or Rr)

Tongue rolling Free hanging ear lobes Hitchhiker’s thumb Almond shaped eyes Full lips Hair on middle section of fingers Huntington’s disease

Section Assessment

Answer questions (1-4) on page 314.

Chapter 12.2 Scientific Terms

1. Incomplete dominance2. Codominant allele3. Multiple allele4. Autosome5. Sex chromosome

5. Describe the concept of “incomplete dominance” and describe an example.

When the phenotype of the heterozygote is a blending of the two homozygotes

Ex: If a red flower (RR) is crossed with a white flower (R’R’), the resulting offspring are heterozygotes (RR’) which look pink

6. Describe the concept of codominance. Show an example.

Codominant alleles cause the phenotypes of both homozygotes to be produced in the heterozygote

Both alleles are expressed equally, not combined

When a black chicken is crossed with a white chicken, the offspring are NOT gray, they are black and white

7. Describe the concept of multiple phenotypes from multiple alleles. Describe the book’s example.

It is common for more than 2 alleles to control one trait

Traits controlled by more than 2 alleles have “multiple alleles”

In pigeons, a single gene that controls feather color has 3 alleles

Ex: BA makes red feathers B makes blue feathers b makes chocolate colored feathers

8. What is the difference between autosomes and sex chromosomes? How do the sex chromosomes affect sex-linked inheritance? Can you think of any sex-linked traits in humans?

Autosomes the 22 pairs of homologous chromosomes besides the sex chromosomes

Sex chromosomes the 2 chromosomes that determine the sex of an individual

Sex-linked traits traits controlled by genes located on the sex chromosomes- the Y chromosome has no corresponding allele to some traits on the X chromosome

Ex: color blindness, male pattern baldness

Review… write answers with SAQs

1. A blue fish and a yellow fish have all green babies! What inheritance pattern does fish color follow?

2. A red cow and a white cow have red & white calves. What inheritance pattern does this follow?

3. What is a chart of chromosomes called?

4. What is II-2’s genotype?

5. What is most likely II-1’s genotype?

Types of Inheritance…

1. Complete dominance2. Incomplete dominance3. Codominance4. Multiple Alleles5. Sex Determination6. Sex-linked inheritance7. Polygenic inheritance8. Environmental Influences

Chapter 12.2 & 3 Terms

1. Sex-linked trait2. Polygenic inheritance3. Karyotype *Turn in terms sheet*

9. Describe what polygenic inheritance is and describe an example.

It is the inheritance pattern of a trait that is controlled by two or more genes

Ex: skin color (AABBCC)- the CAPITAL letters are darkness- the lowercase letters are lightness

AABBCC AaBbCc aabbcc AAbbCcvery dark medium very light medium

10. How does the environment influence genetic expression? Describe the influence of the external and internal environments.

The genetic makeup at fertilization is the potential

Many factors can influence how the gene is expressed (internal and external factors)

External temperature, nutrition, light, chemicals, infections- Ex: tree leaves, height

Internal male vs female due to hormones and structural differences- Ex: horn size, male baldness, peacock feathers

11. Describe what disorder exhibits codominance in humans, and why this is actually an advantage.

Sickle-cell anemia Most common in African-Americans and

white Americans from the Mediterranean About 1 in 12 are heterozygous (RR’) and

produce both normal RBCs and sickle ones Advantage in malaria

12. Describe how multiple alleles govern human blood types, and why this is important to know. ABO blood group Determined by the presence or absence of

surface proteins on RBCs Three alleles for the “I” trait IA, IB, i

Section Assessment

Answer questions (1-4) on page 322

Turn in your Ch 12.2 sheet

Types of Inheritance…

1. Complete dominance2. Incomplete dominance3. Codominance4. Multiple Alleles5. Sex Determination6. Sex-linked inheritance7. Polygenic inheritance8. Environmental Influences

13. Describe the two sex-linked traits talked about in your book. Why do males usually get these disorders?

1. Red-Green color blindness- caused by two recessive alleles at two gene sites on the X chromosome

2. Hemophilia- problem with blood clotting- 1 in 10,000 males - 1 in 100,000,000 females- inherited on X chromosome from mother carriers- treated with blood transfusions and Factor VIII (a blood clotting enzyme)

14. Describe how skin color is considered polygenic inheritance.

There aren’t just light and dark people, there are intermediates also

Ex: light person + dark person = medium peoplemedium + medium = dark, medium, light

The “AABBCC” idea from before

15. What happens when there are changes in the chromosome numbers in humans?

Many abnormal phenotypes result from changes in chromosome numbers

Missing information Too much information Usually results in disorders

16. How do scientists figure out if someone has an unusual number of autosomes?

Normal: 23 pairs (46 chromosomes) 22 pair are autosomes; 1 pair are sex If unusual autosome number, can have

47 or more chromosomes A “karyotype” is a chart of chromosome

pairs from an individual’s cells

17. What happens when an individual has an extra chromosome 21?

Usually disorders of chromosome number cause problems so severe the fetus dies

Down syndrome the only autosomal trisomy where the individual survives into adulthood (1 in 700 births)

It is a trisomy of chromosome 21 Higher incidence in mothers over 40

years

18. Describe the abnormalities that occur when there is an unusual number of sex chromosomes.

The 2 sex chromosomesXX if female and XY if male

An X chromosome can be missing and be XO

An X may be extra and be XXY or XXX An extra Y could be added and have XYY There is not enough information in the Y

to have no X at all YO won’t happen

MiniQuiz

Which inheritance pattern is exhibited by the following:

Red flowers + white flowers = pink flowers Red, blue, and chocolate pigeon feathers Black chicken + white chicken = checkered

chicken Red-green colorblindness & hemophilia Cystic fibrosis & Tay-Sachs disease

Section assessment

Answer questions (1-4) on page 329

The End!