Biologist ___________________________
Date ______________
14-1 PowerPoint - Human Chromosomes
Karyotypes
A ___________ is the full set of genetic information that an organism carries in its DNA.
A study of any genome starts with ___________, the bundles of DNA and protein found in the
nuclei of eukaryotic cells.
Karyotypes
A geneticist will cut out the chromosomes from photographs of cells in ___________ (usually
blood cells) and arrange them in a picture known as a karyotype.
It shows the complete ___________ set of chromosomes grouped together in pairs, arranged in
order of decreasing size.
A karyotype from a typical human cell, which contains ___ chromosomes, is arranged in ___
pairs.
Sex Chromosomes
_____ of the 46 chromosomes in the human genome are known as sex chromosomes, because
they determine an individual’s sex.
Females have two copies of the ___ chromosome.
Males have one ___ chromosome and one ___ chromosome.
Sex Chromosomes
Males and females are born in a roughly ____:____ ratio.
This ensures that just about half the ___________ will be males and half will be females.
Sex Chromosomes
More than _________ genes are found on the X chromosome, some of which are shown.
The human Y chromosome is much smaller than the X chromosome and contains only about
_______ genes, most of which are associated with ________ sex determination and sperm
development.
Autosomal Chromosomes
The remaining ____ human chromosomes are known as autosomal chromosomes, or
autosomes.
The complete human genome consists of _____ chromosomes, including 44 autosomes and 2
sex chromosomes.
To quickly summarize the total number of chromosomes present in a human cell, biologists
write ____________ for females and _____________ for males.
Dominant and Recessive Alleles
Many human traits follow a pattern of ___________ (or simple) dominance.
For example, a gene known as ___________ helps determine skin and hair color.
Red hair results from ___________ MC1R genes while ___________ alleles for the MC1R gene
help produce darker hair colors.
Codominant and Multiple Alleles
The alleles for many human genes display ___________ inheritance.
One example is the _______ blood group, determined by a gene with three alleles: IA, IB, and I
(or A, B, and o)
Sex-Linked Inheritance
The genes located on the ___ and ___ chromosomes show a pattern of inheritance called sexlinked.
A ___________ gene is a gene located on a sex chromosome.
Genes on the ___ chromosome are found only in males and are passed directly from father to
son.
Genes located on the ___ chromosome are found in both sexes, but the fact that men have
just one X chromosome leads to some interesting consequences.
Sex-Linked Inheritance
For example, humans have three genes responsible for ________ vision, all located on the X
chromosome. It affects about 1 in ____ males (red-green colorblindness) and only 1 in _____ females
since females have two X chromosomes.
The recessive phenotype of a sex-linked genetic disorder tends to be much more common
among ___________ than among ___________.
X-Chromosome Inactivation
If just one X chromosome is enough for cells in males, how does the cell “adjust” to the extra
X chromosome in female cells?
In female cells, most of the genes in one of the X chromosomes are randomly switched _____,
forming a dense region in the nucleus known as a ________ body.
Barr bodies are generally _____ found in males because their single X chromosome is still
active.
X-Chromosome Inactivation
X-chromosome inactivation also happens in other mammals.
In _______, a gene that controls the color of coat spots is located on the X chromosome.
Different parts of their body will turn different X chromosomes off or on resulting in a mixture of
orange and _________ spots.
Human Pedigrees
To analyze the pattern of inheritance followed by a particular trait, you can use a chart,
called a pedig___________ ree, which shows the relationships within a family.
A pedigree shows the presence or absence of a trait according to the ___________ between
parents, siblings, and offspring.
Human Pedigrees
The information gained from pedigree analysis makes it possible to determine the ___________
of genes and alleles associated with inherited human traits.
Based on a pedigree, you can often determine if an allele for a trait is ___________ or
___________, ___________ or ___________.
Example #1 – Dominant or Recessive, Sex-linked or Autosomal
Example #2 – Dominant or Recessive, Sex-linked or Autosomal
Example #3 – Dominant or Recessive, Sex-linked or Autosomal