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Spring 2011

Human body cells have __pairs of homologous chromosomes.

Human body cells have 23 pairs of homologous chromosomes.

How many pair of autosomes do human body cells have?

22 pairs of autosomes

# pair of sex chromosomes

1 pair of sex chromosomes

Describe paired autosomes

Paired autosomes (2 autosomes): same in length and shape, have the same centromere location (the place where 2 autosomes connect), carry the same genes along their length ("sister" chromatids)

Describe sex chromosomes

Sex chromosomes: Identical in human females (XX) and Nonidentical in human males (XY)

___gene on the Y chromosome that is the basis of male sex determination.

SRY gene on the Y chromosome is the basis of male sex determination.

What does SRY gene do?

SRY gene on the Y chromosome initiates synthesis of testosterone. Testosterone hormone causes embryo to develop into a male.

What happen if an embryo has no SRY gene?

If an embryo has no SRY gene, it means that it has no Y chromosome-- the embryo will develop into a female.


Diagnostic tool that reveals missing or extra chromosomes and some structural changes in an individual's chromosomes.

When stage of meiosis can one do Karyotping (easier)?

Karyotyping took an image of chromosomes undergoing metaphrase during meiosis.

Describe the evolution of Y chromosome

Some 100s million years ago, sex was determined by temperature. Then the SRY gene developed. 2 chromosomes became more and more distinct. Because the SRY gene is the only necessary part in the Y-chromosome in determining the sex (male), the size of the Y-chromosome decreases until there left the SRY gene and the remaining top of the Y-chromosome, to which the X-chromosome recombines.

Certain mutated forms of alleles on the autosomes give rise to ____.

Certain mutations in the alleles give rise to genetic abnormality or genetic disorders.

X-linked Inheritance Patterns

certain dominant and recessive alleles on the X-chromosome (called X-Linked) are inherited in Mendalian Pattern (table).

Mutated alleles on the X-chromosomes that contribute to a lot of genetic disorders.

Why male can't transmit recessive X-linked alleles to sons

Father only passes down his Y-chromosome to son. The son will get the x-linked chromosome only from the mother.


Failure of one or more pairs of duplicated chromosomes to separate during meiosis (one side has 2 pairs, one side has 1 pair (when the microtubles pull the pairs to either sides of the cell). Chromosome number in gametes are less or more than normal.

This change in chromosome number of a parental cell can be permanent--meaning it will pass on to other generations. Heritable change in chromosome Number.


cells with too many or too few copies of a chromosome.

caused by nondisjunction: failure for one or more pairs of chromosomes to separate during meiosis. the resulting gametes have one more or one less chromosome. (change in chromosome number per gametes than what is normal)

Example of aneuploidy

Down syndrome

Change in chromosome number in gametes is often caused by____.


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