unit 5: heredity Flashcards
how many chromosomes are in a cell?
chromosomes are made up of protein and a single molecule of DNA which is passed from parent to offspring.
there are 23 pairs of chromosomes in human cells.
how does a somatic cell compare to a gamete?
somatic cells have 46 chromosomes while gametes are haploid cells with 23
sex chromosome vs autosome
sex chromosomes determine the sex of an individual. an autosome is a chromosome not involved in determining sex
karyotypes
A karyotype is a display of the chromosome pairs of a cell arranged by size and shape. Karyotypes are prepared from isolated somatic cells which are treated with a drug to stimulate mitosis and then they are grown in culture for several days. Cells arrested when chromosomes are most condensed (metaphase) are stained and then viewed with a microscope. Karyotypes help determine the size of the chromosome, position of the centromere and pattern of stained bands to help identify specific chromosomes.
homologous chromosomes
a pair of chromosomes of the same length, centromere position, and staining pattern that possesses the genes for the same characters at the corresponding loci. one is inherited from the mother and one from the father
where are gametes produced?
in the gonads (germ cells): testes and ovaries // anther and ovule
meiosis
Gametes are produced through meiosis: a type of cell division sexually reproducing organisms with two rounds of cell division but only one round of DNA replication. It produces gametes and enhances genetic variability.
what are alleles?
any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
ex) freckles, hair color
what is synapsis?
the pairing and physical connection of duplicated homologous chromosomes
what is crossing over?
crossing over produces recombinant chromosomes (individual chromosomes that carry genes from two different parents)
an average of one to three crossover events occurs per chromosome pair, depending on the size of the chromosomes and the position of their centromeres
when do crossing over and synapsis occur?
Prophase I
explain the difference between a monohybrid and dihybrid cross?
cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters)
Law of Independent Assortment
cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
Incomplete dominance
ncomplete dominance: neither allele is completely dominant, offspring have a phenotype between the parents (red and white flowers having a pink offspring)
complete dominance
Complete dominance: phenotypes of the heterozygotes and the dominant homozygotes are indistinguishable (red is dominant over white and produces red offspring)
pleiotrophy
Most genes have pleiotrophy (i.e. multiple phenotypic effects). In humans, pleiotropic alleles are responsible for the multiple symptoms associated with certain hereditary diseases, such as cystic fibrosis and sickle-cell disease. Cystic fibrosis affects the cells responsible for producing mucus, sweat, and digestive juices (one gene influencing two or more seemingly unrelated phenotypic traits). Similarly, sickle cell is a pleiotropic disease because the expression of a single mutated HBB gene produces numerous consequences throughout the body.
epistasis
a type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene
cystic fibrosis
recessively inherited, defective membrane protein for chloride, mucus builds up in lungs, pancreas, digestive tract, poor absorption of nutrients, chronic bronchitis, infections, premature death
sickle-cell disease
recessively inherited; low oxygen content leads to deformed red blood cells; clumping and clogging of cells, physical weakness, pain, organ damage even paralysis and brain damage.
achondroplasia
dominantly inherited, heterozygotes, have dwarf phenotype, bone defects, 99.99% of population have homozygous recessive genotype
huntington’s disease
dominantly inherited, degenerative disease of nervous system, movement and psychiatric
chromosome theory of inheritance
genes have specific loci along chromosomes, and these chromosomes undergo segregation and independent assortment
law of segregation
when an organism makes gametes, each gamete receives just one gene per copy which is selected randomly
why is the fruit fly an excellent subject for genetic studies?
a) single mating will produce hundreds of offspring
b) a new generation can be bred every two weeks
c) the fruit fly has only four pairs of chromosomes, which are easily distinguishable with a light microscope
SRY gene
SRY refers to the Sex determining Region of Y, a gene found on the Y chromosome that is required for the development of testes
sex-linked gene
A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome
What is a Barr body?
A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed inactivated X chromosome. Female mammals, including humans, inherit two x chromosomes- twice the number inherited by males; females show a Barr body in their cells to that the cells of females and males have the same effective dose (one copy) of most x-linked genes
How is the X chromosome inactivated?
The selection of which X chromosome will form the Barr body occurs randomly and independently in each embryonic cell present at the time of X inactivation. Females consist of a mosaic of two types of cells; those with the active X derived from the father and those with the active X derived from the mother. After an x chromosome is inactivated in a particular cell, all mitotic descendants of that cell have the same inactive X.
nondisjunction
an error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other
aneuploidy
a chromosomal aberration in which one of more chromosomes are presnet in extra copies or are deficient in number (Ex Trisomy 21)
monosomy
refers to a diploid cell that has only one copy of a particular chromosome instead of the normal two. Turner syndrome is a human monosomy, the female has only one X chromosome
trisomy
trisomy - refers to a diploid cell that has three copies of a particular chromosome instead of the normal two. Trisomy is trisomic for chromosome 2
polyploidy
a chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.
