Section 14-1 Human Heredity

Section 14-1 Human Heredity

Human Heredity Human Chromosomes 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 : X and Y chromosomes = sex chromosomes: determine individuals 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? Many human genes have become known through the study of genetic disorders. true

Genetic Disorder 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 Huntingtons

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 sickle-shaped 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 genes 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.

: Is the following sentence true or false? The Y chromosome does not contain any genes at all. False : 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 If you saw a white cat with orange

and black spots, is it most likely a male or a female? Its 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

The Y chromosome contains a sex-determining region that is necessary for male sexual development, but without an X chromosome the embryo doesnt develop properly. We need X to survive,

but not the Y chromosome.

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