Karyotypes and Inheritance

karyotype

the complete set of chromosomes in an organism, arranged and displayed in pairs based on size, shape, and banding pattern

autosomes

also known as body chromosomes; the chromosomes besides the sex chromosomes

23, 46

Humans have __ pairs of chromosomes and __ in total.

sex chromosomes

Out of the 23 pairs of chromosomes that humans have, 1 pair is the ___ ________. XY genetically leads to male development and XX genetically leads to female development.

nondisjunction

the improper separation of homologous chromosomes during meiosis

One gamete receives two of the same type of chromosome and another gamete receives no copy of that chromosome.

What results from nondisjunction?

mistakes during chromosome repair or cell division

What are chromosomal block mutations caused by?

duplication

a segment is copied, resulting in duplicate sections and potentially increases gene expression

deletion

a segment is removed (genes in removed segment are lost)

inversion

a segment is flipped in reverse order (may not be readable anymore)

translocation

segments of two chromosomes are exchanged (may interrupt gene sequences)

trisomy 21/down syndrome

This non-disjunction disorder results in individuals with 47 chromosomes. It happens in 1 in 700 births in all populations

locus

position of a gene on a chromosome

gene

a segment of DNA that carries the genetic code/instructions to make specific proteins. they are located on chromosomes and each chromosome is made up of long strands of DNA, within this DNA are multiple ____.

genotype

combination of alleles that an individual inherits for a given gene

phenotype

the physical characteristics of an organism that depend on how the organism’s genotype is expressed

1 allele

How many alleles do organisms have for each gene on one chromosome? (Hint: 2 alleles for each gene in homologous chromosome pairs)

dominant allele

allele that masks the presence of another allele for the same gene when they occur together in a heterozygote

recessive allele

allele that is masked by the presence of another allele for the same gene when they occur together in a heterozygote. when in a homozygote, the allele is not masked.

incomplete dominance

neither allele trait shows. instead, typically an intermediate/blended phenotype of the two parental allele traits shows because neither allele is completely dominant over the other).

ex: a red flower (RR) and a white flower (WW) cross and produce a pink flower (RW)

co-dominance

both allele traits are shown equally (50% and 50%), neither allele is completely dominant over the other

ex: father has a homozygous I^AI^A genotype, a mother has a homozygous I^BI^B genotype, the offspring has both I^AI^B

mendel’s law of segregation

the 2 copies of a gene are separated during meiosis and end up in different gametes. as a result, each gamete gets only one allele from each gene pair

Each gamete only receives 1 allele for each gene due to segregation of homologous chromosomes during meiosis (Anaphase I)

What is the cell basis of Mendel’s law of segregation?

mendel’s law of independent assortment

each pair of alleles segregates independently of other pairs of alleles during gamete formation; the inheritance of one character has no effect on the inheritance of another

Different type of chromosomes segregate independently of each other during meiosis (Anaphase I)

What is the cell basis of Mendel’s law of independent assortment?

sex-linked genes

genes located on the sex chromosomes

• 2 alleles for each gene

• 1 allele is dominant

• 1 allele is recessive

What are the Mendelian traits?

complex inheritance

inheritance patterns that do not follow Mendelian principles

pleiotropy

1 gene codes for multiple characteristics

(e.g. sickle cell disease, one gene called the hemoglobin gene affects multiple parts of the body and codes for the various symptoms of the disease such as resistance to malaria and the dysfunction of red blood cells.)

polygenic

many genes code for 1 trait

(e.g. hair color, skin color)

linked genes

genes located on the same chromosome

linkage map

Linkage can be assessed by determining how often crossing over occurs between two genes on the same chromosome. Genes on different (nonhomologous) chromosomes are not linked…..The lower the frequency of crossing over, the closer together on the same chromosome the genes are presumed to be. Frequencies of crossing over can be used to construct a _______ ____ which shows the locations of genes on a chromosome.

hemophilia

a genetic disorder where blood doesn't clot properly due to a deficiency in clotting factors, leading to prolonged bleeding