Chapter 12 Inheritance Q&A. Gregor Mendal Father of Genetics Garden pea plants Flowering plants have male and female parts Looked at hybrids from true-breeding

Chapter 12Inheritance Q&A

Gregor Mendal

• Father of Genetics• Garden pea plants• Flowering plants have male and female parts• Looked at hybrids from true-breeding plants

What determines a person’s sex?• Humans have 23 pairs of chromosomes.– 22 pairs are autosomes.– 1 pair are sex chromosomes.

What determines a person’s sex?

• The presence of a Y chromosome signals the male developmental pathway during fetal development.– Males are XY.


• Sons inherit one Y chromosome from their father and one X chromosome from their mother.


• Daughters inherit one X chromosome from their mother and one X chromosome from their father.– Females are XX.


• Fathers determine the sex of a baby based on whether the sperm fertilizing a mother’s egg carries an X or a Y sex chromosome.– The SRY gene on the Y chromosome signals testes

to develop.

What determines a person’s sex?• An intersexual person has external genitalia

that do not match his or her internal sex organs.

Why do some genetic conditions affect sons more often than daughters?

• An X-linked trait is a phenotype that is determined by an allele on an X chromosome.


• For a recessive X-linked trait, a normal copy on one X chromosome masks the recessive disease allele on the other X chromosome.


• A male has a single X chromosome, so he will show the effects of any recessive alleles located on his X chromosome.


• A female can carry the disease allele without showing it.- Duchenne Muscular Dystrophy


• A woman always passes one of her X chromosomes to each of her children.

• A man passes his single X chromosome to his daughters and his Y chromosome to his sons.

How can Y chromosomes be used to trace paternity and ancestry?

• Y-chromosome analysis is used to study ancestry and to identify paternity in order to verify, discredit, or fill in missing pieces of historical information.


• Sons inherit their Y chromosome from their biological fathers.– Since Y chromosomes have no homologous

partner chromosome with which to pair during meiosis, the Y chromosome rarely undergoes genetic recombination.


• Short tandem repeats (STRs) on the Y chromosome can be studied to show that two men have the same Y chromosome.

What is incomplete dominance?• Incomplete dominance is a form of inheritance in which

heterozygotes have a phenotype that is intermediate between homozygous dominant and homozygous recessive.

What is codominance?• Codominance is a form of inheritance in

which both alleles contribute equally to the phenotype.

Codominance and blood typing

• There are three basic blood group alleles: A, B, and O. We inherit one allele from each parent.

– The possible combinations of the three alleles are OO, AO, BO, AB, AA, and BB.


• Blood type alleles A and b are codominant, while O is recessive to both A and B.


• The positive Rh factor allele (Rh+) is dominant over the recessive Rh factor allele (Rh-).

Blood transfusions

• The ability to donate or receive blood is based on immune rejection.

Comparing incomplete dominance and codominance

• In incomplete dominance, heterozygotes display an intermediate phenotype.

• In codominance, heterozygotes display both phenotypes.

What is a polygenic trait?

• A polygenic trait is a single trait whose phenotype is determined by the interaction between alleles of more than one gene.- skin color

Environmental factors can also influence some phenotypes

• When an interaction between genes and the environment contributes to a phenotype or trait, the trait is multifactorial.

Errors in meiosis• Nondisjunction is a failure of chromosomes to separate

accurately during cell division. This occurrence leads to aneuploidy – an abnormal number of one or more

chromosomes.

Errors in meiosis

• When an aneuploid gamete is fertilized by a normal gamete, the resulting zygote can have an abnormal number of chromosomes.

Fetal chromosomal abnormalities

• In most cases, fetal chromosomal abnormalities are so severe the zygote spontaneously aborts.

• In some cases, the abnormality is not life- threatening but does cause a severe disability.


• Trisomy 21, also known as Down syndrome, results when an embryo inherits an extra copy of chromosome 21.


• Down syndrome and other chromosomal abnormalities can be diagnosed by amniocentesis, a procedure that removes fluid surrounding the fetus to obtain and analyze fetal cells to diagnose genetic disorders.


• Technicians analyze the fetal karyotype (the chromosomal makeup of cells) using the amniotic fluid that contains fetal cells with the fetus’s DNA.

What are stem cells?• Stem cells are

immature cells that can divide and differentiate into specialized cell types.

Stem cells keep tissues healthy

• Most body tissues contain stem cells that help regenerate those tissues and organs.

Using stem cells to build new organs

• Organisms use cell division to replace old cells. Engineering human tissue takes advantage of this process.

Adult stem cells• Specific stem cells

are responsible for specific tissue types.

• Adult stem cells, or somatic stem cells, are stem cells located in tissues that help maintain and regenerate those tissues.

Not all stem cells are created equal

• Some stem cells are pluripotent – they can differentiate into nearly any cell type in the body.

• Some stem cells are totipotent – they can differentiate into any of the body’s cell types.

Not all stem cells are created equal

• Embryonic stem cells are found in the blastocyst stage (the stage of embryonic development in which the embryo is a hollow ball of cells) of an early embryo. Depending on the stage of embryonic development, embryonic stem cells may be either totipotent or pluripotent.

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Chapter 12 Inheritance Q&A. Gregor Mendal Father of Genetics Garden pea plants Flowering plants have male and female parts Looked at hybrids from true-breeding