Transcript Mendel and Heredity

Meiosis and Mendel
Chapter 6.1-6.3
KEY CONCEPT
Gametes have half the number of chromosomes that body cells
have.
You have body cells and gametes.
• Body cells are also called somatic cells.
• Germ cells develop into gametes.
– Germ cells are located in the ovaries and testes.
– Gametes are sex cells: egg and sperm.
– Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)
Your cells have autosomes and sex
chromosomes.
•
•
•
Your body cells have 23 pairs of
chromosomes.
– Homologous pairs of
chromosomes have the same
structure.
– For each homologous pair, one
chromosome comes from each
parent.
Chromosome pairs 1-22 are
autosomes.
Sex chromosomes, X and Y,
determine gender in mammals.
Body cells are diploid;
gametes are haploid.
• Fertilization between egg and sperm occurs in
sexual reproduction.
• Diploid (2n) cells have two copies of every
chromosome.
– Body cells are diploid.
– Half the chromosomes come from each parent.
•
Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex chromosome.
•
Chromosome number must be maintained in animals.
•
•
Many plants have more than two copies of each chromosome.
Mitosis and meiosis are types of nuclear division that make different
types of cells.
Mitosis makes
more diploid cells.
•
•
Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
•
Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in diploid cells.
What is heredity?
• The passing on of
characteristics (traits) from
parents to offspring
• Genetics is the study of
heredity
KEY CONCEPT
Mendel’s research showed that traits are inherited as discrete units.
Mendel laid the groundwork for
genetics.
• Traits are distinguishing
characteristics that are
inherited.
• Genetics is the study of
biological inheritance
patterns and variation.
• Gregor Mendel showed that
traits are inherited as
discrete units.
• Many in Mendel’s day
thought traits were blended.
Mendel’s experiment
• Go to film clip from biology text book
Mendel used peas...
• They reproduce sexually
• They have two distinct, male
and female, sex cells called
gametes
• Their traits are easy to
isolate
Mendel crossed them
• Fertilization - the uniting of
male and female gametes
• Cross - combining gametes
from parents with different
traits
Mendel’s data revealed patterns of
inheritance.
• Mendel made three key decisions in his
experiments.
– use of purebred plants
– control over breeding
– observation of seven
“either-or” traits
•
Mendel used pollen to fertilize selected pea plants.
– P generation crossed to produce F1 generation
– interrupted the self-pollination process by removing male flower parts
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
•
Mendel allowed the resulting plants to self-pollinate.
– Among the F1 generation, all plants had purple flowers
– F1 plants are all heterozygous
– Among the F2 generation, some plants had purple flowers and some had
white
•
Mendel observed patterns in the first and second generations of his crosses.
•
Mendel drew three important conclusions.
– Traits are inherited as discrete units.
– Organisms inherit two copies of each gene, one from each parent.
– The two copies segregate
during gamete formation.
– The last two conclusions are
called the law of segregation.
purple
white
What Did Mendel Find?
• He discovered different laws
and rules that explain
factors affecting heredity.
Rule of Unit Factors
• Each organism has two
alleles for each trait
• Alleles - different forms of
the same gene
• Genes - located on
chromosomes, they control
how an organism develops
Rule of Dominance
• The trait that is observed in
the offspring is the dominant
trait (uppercase)
• The trait that disappears in
the offspring is the
recessive trait (lowercase)
Law of Segregation
• The two alleles for a trait
must separate when gametes
are formed
• A parent randomly passes
only one allele for each trait
to each offspring
Law of Independent
Assortment
• The genes for different
traits are inherited
independently of each other.
Phenotype & Genotype
• Phenotype - the way an organism
looks
• red hair or brown hair
• genotype - the gene combination
of an organism
• AA or Aa or aa
Heterozygous & Homozygous
• Heterozygous - if the two
alleles for a trait are different
(Aa)
• Homozygous - if the two alleles
for a trait are the same (AA or
aa)
Dihybrid vs Monohybrid
• Dihybrid Cross - crossing
parents who differ in two
traits (AAEE with aaee)
• Monohybrid Cross - crossing
parents who differ in only
one trait (AA with aa)