chapter 15: chromosomal basis of inheritance

parental type

phenotype of the parents

recombinant

the offspring having a different phenotype than either of the parents

aneuploidy

abnormal number of a particular chromosome

monosomy

zygote only has one copy of an chromosome

trisomy

zygote has an extra copy of a chromosome

polyploidy

organism has more than 2 sets of chromosomes

deletion

nucleotide base removed from DNA strand

duplication

nucleotide base duplicated in a DNA strand

inverstion

set of nucleotides are inverted

translocation

set of nucleotides from different DNA strand is inserted into a new strand

sex-linked gene

a gene is located on a sex chromosome

why most genetic disorders are on the x chromosome

the x chromosome is larger than the Y chromosome, therefore can carry more genes

x-inactivation and barr body

• x inactivation occurs in every somatic cell in a human woman. it’s when one of the x chromsomes is inactivated/condensed because there it already a copy of it

• barr body is the name of a condensed chromosome

what is a “carrier”

it means you are heterozygous for a recessive disorder

recombination frequency

(# recombinant) / (# total offspring)

linkage map units

determined by the frequency of the genes occurring together

if the recombination frequency is less than 50%….

…then the genes are most likely on the same chromosome

how do recombinants appear if two genes are on the same chromosome

crossing over

nondisjunction and consequences

• sister chromatids or homologous chromosomes not separating in meiosis

• genetic disorders from having additional chromosome or lacking a chromosome

nondisjunction in meiosis 1 vs meiosis 2

• meiosis 1: occurs when homologous chromosomes don’t separate properly. causes all gametes in the 4 daughter cells to be affected

• meiosis 2: occurs when sister chromatids do not separate properly. causes the 2 daughter cells to be affected

chromosomal alteration types

insertion, deletion, translocation, duplication

down syndrome

occurs when someone has 3 copies of chromosome 21

klinefelter syndrome

a male has 2 x chromosomes (XXY)

turner syndrome/ monosomy x

a female is missing an x chromosome (X0)

genomic imprinting

the maternal allele and paternal allele are distinguished and only one is used, silencing the other.

why some disease come from female even though not on X

because the organelles are donated by the mother, not the father