Transcript LN #18 Heredity

Heredity
LN #18
California Content Standard
Genetics
2g. Students know how to predict possible combinations of alleles in a zygote from
the genetic makeup of the parents.
What is Meiosis?
• Meiosis makes SEX
CELLS.
– Haploid cells
– Gametes
– Sperm & egg cells
• Diploid is 2n
– All of our body cells
are diploid.
• Haploid is n
– ONLY gametes are
haploid.
fertilization
+
=
What is a Phenotype?
• A phenotype
describes what an
organism looks like.
• In order to determine
an organisms
phenotype you need
to look at it.
Phenotype =
widow’s peak
Phenotype =
free earlobes
Phenotype =
attached
earlobes
What is a Genotype?
Gene location
for earlobes.
• A genotype is the
combination of genes in
an organism.
F
f
• Genes are section of
DNA that codes for a trait.
free
attached
Genes are located on
chromosomes.
F and f are
Genotype =
• Alleles are different
alleles.
Ff
forms of a gene.
• Genes are labeled by
using letters.
Homologous chromosomes
have genes for the same trait.
Who was Gregor Mendel?
• Mendel carried out the
first important studies in
heredity.
• Mendel studied heredity
using pea plants.
• Mendel was the first to
develop laws and rules
for heredity.
• One of Mendel’s rules is
the rule of dominance.
– Some traits are dominant
and others are recessive.
(1822 – 1884)
Punnett Squares
• Punnett squares are used
to determine the chance
of seeing a trait in the
offspring.
• Remember every
organism has two copies
of a gene. Only one of
the two is passed to the
offspring.
• If the genotype of a father
is Aa, then he can either
pass down A or a.
Words to know
• Monohybrid cross involves studying a single
trait.
• Homozygous means that both alleles are the
same. We can have homozygous dominant, TT
or homozygous recessive tt.
• Heterozygous means that the alleles are
different from one another. We would have Tt.
• With the rule of dominance TT and Tt have the
same phenotype. The only way to show a
recessive trait is to be homozygous recessive, tt.
Monohybrid Cross problem
• Widow’s peak is a
Parent’s genotype
dominant trait (P).
• A woman
P
homozygous
dominant for widow’s
p
peak marries a man
Pp
without a widow’s
peak. What are the
chances that their
Pp
children will have a
p
widow’s peak?
PP x pp
P
Pp
Pp
100% chance that the children will
have a widow’s peak.
Summary
•
•
•
•
•
What is a genotype and phenotype?
Who was Mendel?
What are Punnett squares used for?
What are alleles?
How are homozygous and heterozygous
different?