IB BIOLOGY GENETICS

48 terms by annguyen316

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genetics

Gene

a heritable factor that controls a specific characteristic.

Allele

one specific form of a gene, differeing from other alleles by one or a few bases only and occupying the same locus as other alleles of the gene.

Genome

The whole of the genetic information of an organism

gene mutation

a change in the base sequence of a gene.

Base substitution

The smallest possible change is when one base in a gene is replaced by another. An example of this type of mutation is sickle cell anemia

Meiosis

a reduction division of a diploid nucleus to form haploid nuclei.

Homologous chromosomes

chromosomes with the same genes in the same loci but not necessairly the same alleles of those genes.

Random orientation

during prophase I the position of each pair of chromosomes when the spindle attaches is random

Non-disjunction

sometimes chromosomes that should separate and move to opposite poles during meiosis do not separate and instead they both move to the same pole

Karyotyping

chromosomes are arranged in pairs according to their size. Peformed using cells collected by chorionic villus sampling for prenatal diagnosis of chromosome abnormalities.

Prophase I

Chromosome supercoil, homologous chromosomes (bivalents) pair up (synapsis), crossing over occurs resulting in chiasma, centrioles move to opposite poles in animal cells and the nuclear membrane reaks down.

Metaphase I

spindle microtubules attach to centromeres, bivalents line up at the equator.

Anaphase I

the two chromosomes of each bivalent move to opposite poles, thus halving the chromosome number, each chromosome consists of two identical sister chromatids, if crossing over occured they are not identical.

Telophase I

nuclear membrances form, the cel divides to form two haploid cells

Prophase II

Chromosome supercoil, homologous chromosomes (bivalents) pair up (synapsis), crossing over occurs resulting in chiasma, centrioles move to opposite poles in animal cells and the nuclear membrane reaks down. [EXCEPT THERE ARE NO HOMOLOGOUS CHROMOSOMES TO PAIR UP, THUS NO CROSSING OVER]

Metaphase II

spindle microtubules attach to centromeres, bivalents line up at the equator, at the end of the phase the centromeres divide.

Anaphase II

The centromeres spilt, then the two chromatids of each chromosome move to opposite poles

Telophase II

nuclear membrances form, the cel divides to form two haploid cells [EXCEPT TWO CELLS DIVIDE TO FORM FOUR HAPLOID CELLS WHICH WILL DEVELOP INTO GAMETES, THE CHROMATIDS ARE NOW KNOWN AS CHROMOSOMES

synapsis

during crossing over in prophase I, all the chromatids of two homologous chromosomes become tightly paired.

chiasma

where there was crossing over there is an x-shaped structure

recombination

the reassortment of genes or characters into different combinations from those of the parents

Independent assortment

the way one pair of homologous chromosome is segregated (assorted) during formation of gametes (meiosis) is independent of the way any other pair is segregated. (due to random orientation)

autosome

a chromosome that has no genes involved with sex determination. Humans have 22 pairs.

Sex chromosome

a chromosome that has genes involved with sex determination. Humans have 1 pair.

Linkage group

all of the genes that have their loci on the same chromosome.

Polygenic inheritance

inheritance of characteristics controlled by more than one gene.

Genotype

the alleles of an organism

Phenotype

the characteristics of an organism.

Dominant allele

an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state

Recessive alle

an allele that only has an effect on the phenotype when present in the homozygous state

Codominant allele

pairs of alleles that both affect the phenotype when present in a heterozygote

Locus

the particular position on homologous chromosomes of a gene

homozygous

having two identical alleles of a gene

heterozygous

having two different alleles of a gene.

carrier

an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele

test cross

testing a suspected heterozygote by crossing it with a known homozygous recessive

multiple alleles

some genes have more than two alleles

ABO blood group

are an example of codominance and multiple alleles

blood type O

ii

blood type A

I^AI^A or I^Ai

blood type B

I^BI^B or I^Bi

blood type AB

I^AI^B

sex linkage

the association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome. (usually the X)

Hemophilia

are produced by a recessive sex allele on the X chromosome. The allele is X^h and the dominant allele is X^H

colorblindness

are produced by a recessive sex allele on the X chromosome. The allele is X^b and the dominant allele is X^B

PCR (polymerase chain reaction)

is used to copy and amplify minute quantities of DNA/

Gel electrophoresis

fragments of DNA move in an electric field and are separated according to their size.

Clone

a group of genetically identical organisms or a group of cells derived from a single parent.

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