Human Heredity Human Chromosomes How do biologists make

Human Heredity

Human Chromosomes 쓰지마 �How do biologists make a karyotype? �They photograph cells in mitosis, cut out the chromosomes from the photographs, then group the chromosomes together in pairs.

Human chromosomes 쓰세요: X and Y chromosomes = sex chromosomes: determine individual’s sex. Autosomes are all chromosomes, except the sex chromosomes.

How the sex chromosomes segregate during meiosis. All egg cells have a single X chromosome. …but, half of all sperm cells carry an X chromosome and half carry a Y chromosome.

What does a pedigree chart show? � It shows the relationships within a family.

Some human traits not from single genes. • Many traits are polygenic. • Many traits are influenced by environmental factors.

Human Genes

Why is it difficult to study the genetics of humans? • Humans have: • long generation times, • a complex life cycle, • and relatively few offspring.

Human blood group genes: • The Rh blood group is determined by a single gene. • Individuals with type O blood are homozygous for the i allele (ii) and produce no antigen on the surface of red blood cells.

Is the following sentence true or false? 쓰지마 • Many human genes have become known through the study of genetic disorders. • true

Genetic Disorder 쓰세요 �Tay-Sachs disease � Nervous system breakdown caused by an autosomal recessive allele

Genetic Disorder � Achondroplasia � A form of dwarfism caused by an autosomal dominant allele

Genetic Disorder �Phenylketonuria (PKU) �A buildup of phenylalanine caused by an autosomal recessive allele �need to follow a diet that limits phenylalanine

Genetic Disorder �Huntington’s disease �A progressive loss of muscle control and mental function caused by an autosomal dominant allele

FROM GENE TO MOLECULE �What is the normal function of the protein that is affected in cystic fibrosis? �The protein allows chloride ions to pass across biological membranes.

FROM GENE TO MOLECULE �A change in just one DNA base for the gene that codes for the protein ____causes sickleshaped red blood cells. �HEMOGLOBIN

FROM GENE TO MOLECULE �What is the advantage of being heterozygous for the sickle cell allele? �People who are heterozygous are generally healthy and are resistant to malaria.

FROM GENE TO MOLECULE What makes an allele dominant, recessive, or codominant? �It depends on the nature of the gene’s protein product and its role in the cell.

Human Chromosomes

Human Genes and Chromosomes �Only 2% of DNA in your chromosomes function as genes. �Human genes located close together on the same chromosome tend to be inherited together.

Sex-Linked Genes What are sex-linked genes? �They are genes that are located on the X or Y chromosomes.

쓰지마: Is the following sentence true or false? The Y chromosome does not contain any genes at all. False

쓰세요: Compare-and-contrast table for sex-linked genes.

Is the following sentence true or false? �All X-linked alleles are expressed in males, even if they are recessive. � true

Punnett Square below example: male colorblindness inheritance. (Recessive)

X-Chromosome Inactivation �How does the cell “adjust” to the extra X chromosome in female cells? � In female cells, one X chromosome is switched off.

What is a Barr body? �It is a dense region in the nucleus that is formed by the turned-off X chromosome.

Is the following sentence true or false? �Barr bodies are found only in males. �False �Females have the extra X

쓰지마 �If you saw a white cat with orange and black spots, is it most likely a male or a female? �It’s probably a female. In cells in some parts of the body, one X chromosome that has the allele for orange spots is switched off, whereas in cells in other parts of the body, the other X chromosome with the allele for black spots is switched off.

Chromosomal Disorders What occurs during nondisjunction? �Homologous chromosomes fail to separate during meiosis.

Chromosomal Disorders Is the following sentence true or false? � If nondisjunction occurs, gametes may have abnormal numbers of chromosomes. �True

Chromosomal Disorders �The condition in which an individual has three copies of a chromosome is known as trisomy , which means “three bodies. ”

Chromosomal Disorders �Is the following sentence true or false? �Down syndrome occurs when an individual has two copies of chromosome 21 �False (three copies = trisomy)

�Circle the letter of the characteristic of Down syndrome. b. mental retardation

Chromosomal Disorders Why does an extra copy of one chromosome cause so much trouble? �Scientists do not exactly know for sure.

Chromosomal Disorders Sex chromosome disorders. �Turner syndrome: A female with the karyotype 45, X has inherited only one X chromosome and is sterile.

Chromosomal disorders 쓰지마 �The Y chromosome contains a sexdetermining region that is necessary for male sexual development, �…but without an X chromosome the embryo doesn’t develop properly. We need X to survive, but not the Y chromosome.