Chromosomes, Karyotypes and genes

1
Chromosomes, Karyotypes and genes

• Mrs. Stewart
• Honors Biology
• Central Magnet School

2
Standards

• CLE 3210.4.2 Describe the relationships among
  genes, chromosomes, proteins, and hereditary
  traits.

3
Objectives (today, we will)

• Build a karyotype
• Examine karyotypes to determine the presence or
  absence of genetic disorders
• Analyze the gene that determines sex of offspring
• Use the effects of crossing over to determine
  gene linkage

4
Chromosome Structure

• Chromosome definition

in a eukaryotic cell, one of the structures in
the nucleus that are made up of DNA and protein
in a prokaryotic cell, the main ring of DNA
5
Chromosome Vocabulary

• Histones
• Chromatid
• Centromere

a type of protein found in the chromosomes of
eukaryotic cells but not prokaryotic cells.
one of the two strands of a chromosome that
become visible during meiosis or mitosis
The region of the chromosome that holds the two
sister chromotids together during mitosis
6
Chromosomes

• What do they look like?
• How many do humans have?

They look like an X just before the cell
divides and an I after they divide.
23 Pairs of chromosomes (23 from mom, 23 from dad)
7
Chromosome or Chromatin?

• Chromosome
• Chromatin

Tightly coiled DNA proteins during cell
division DNA cannot be read while in this form.
Loosely coiled DNA proteins during the cells
life other than cell division. DNA can be read
to direct activities of the cell.
8
With your partner

• Do more complex organisms have more chromosomes?

9
With your Partner

• Does every cell have 46 chromosomes?

10
Cell Typesbased on chromosome number

• Diploid 2n (adj)
• Haploid n (adj)
• Visual clip from book

Describes a cell with two copies of each type of
chromosome. Example Animal body cells.
Describes a cell with one set of
chromosomes. Example sex cells (sperm egg)
all prokaryotes (bacteria)
11
What is it?

• Karyotype

an array of the chromosomes found in an
individuals cells at metaphase of mitosis and
arranged in homologous pairs and in order of
diminishing size
12
What can a karyotype tell us?

• Determine sex
• Diagnose some genetic disorders
• Extra chromosomes or pieces
• Missing chromosomes or pieces

13
Chromosomes

• Dark Bands

Are unique to each type of chromosome they are
genes.
14
Types of Chromosomes

• Sex Chromosomes
• Autosome
• Homologues

In animals this pair of chromosomes determine the
gender of the animal
Any chromosome that is not a sex chromosome.
Homologous chromosomes that have the same
sequence of genes, that have the same structure,
and that pair during meiosis
15
How do chromosomes pair on a karyotype?
With their homologue.
16
Karyotype activity

• http//learn.genetics.utah.edu/content/begin/trait
  s/karyotype/

17
What makes a boy become a boy?

• Like other homologues, the sex chromosomes pair
  during Meiosis I
• What are the chances of a sperm cell receiving a
  Y chromosome?
• Sex determination
• Sex determining Region Y or SRY
• Protein that causes gonads of embryo to develop
  as testes

5050
18
Sex-Linked Genes and Traits

• Traits that are coded for by an allele on a sex
  chromosome

19
Which gender displays recessive sex-linked
disorders more often and why?
20
Meiosis Gone Wrong

• Nondisjunction homologous chromosomes fail to
  separate during Meiosis.
• This results in a gamete that will carry too many
  or too few chromosomes.

21
Gene Linkage

• Geneticists hypothesized that genes inherited
  together, must occur on the same chromosome.
• Fly body color
• Fly eye color
• Fly wing type
• Pairs of genes that tend to be inherited together
  are called linked.
• Gene linkage visual concept

22
How do we know where the genes are on a
chromosome, in relation to each other?

• Gene loci (locations) can be determined based on
  crossing-over frequencies
• The cross-over percentage determines the number
  of map units apart

23
Chromosome Mapping

• A chromosome map is a diagram that shows the
  linear order of genes on a chromosome.
• Map unit one percent frequency of cross-over
  unit
• Crossing over visual concept
• Chromosome map visual concept

24
Exit Ticket

• m.socrative.com
• Room stewart348