Transcript Mendel’s Legacy

Mendel’s
Legacy
Chapter 9-1
Heredity
• Heredity is the transmission of characteristics
from parents to offspring
• Mendel observed pea plants and wanted to
explain variations (performed experiments)
• Concluded that
Conclusions
• There is a dominant (masking, capital letter) and
recessive (masked but can reappear, lowercase
letter) factors
– Called alleles
• Offspring receives 1 allele from each parent
• Law of segregation- alleles for same trait are
separated in gametes (sex cells aka egg and sperm)
– Mom and dad gene go in different directions
• Law of independent assortment- alleles for
different traits are separated randomly
– Have different genes from both mom and dad in gamete
Genetic Crosses
Chapter 9-2
Genotype and Phenotype
• Genotype is the genetic
makeup
– Represented by letters: PP,
Pp, pp
• Phenotype is the
appearance: purple, white
• Homozygous is when both
alleles are the same (pp
or PP)
• Heterozygous is when
alleles are different (Pp)
Predicting Results of
Monohybrid Crosses
• Monohybrid cross is a
cross with one pair of
traits
• Dihybrid cross is a cross
with two pairs of traits
– Use a Punnett Square to
predict offspring
rryy
b
b
B
Bb
Bb
B
Bb
Bb
RRYY
ry
ry
ry
ry
RY
RrYy RrYy RrYy RrYy
RY
RrYy RrYy RrYy RrYy
RY
RrYy RrYy RrYy RrYy
RY
RrYy RrYy RrYy RrYy
Predicting Results of
Monohybrid Crosses
• Complete dominance heterozygous and
homozygous dominant look the same
• Incomplete dominance is when both alleles
(heterozygous) influence appearance
– Ex: Red allele and white allele make pink
• Codominance is when both alleles
(heterozygous) are expressed but do not blend
– Ex: Brown and black coat on dog
Incomplete
Dominance
R
r
R
RR
Rr
r
Rr
rr
Codominance
R
R
r
Rr
Rr
r
Rr
Rr
Chromosomes
and
Inheritance
Chapter 12-1
Sex Determination
• X is female and Y is male (smaller
chromosome)
• After meiosis II, one cell gets X and one get Y
(from male parent)
• 50% chance of being male or female
• Sex linked traits on X or Y chromosome
Linkage Groups
• Genes located on one chromosome and are
inherited together
• Crossing over is the exchange of genes
– Causes new gene combinations
Cell Mutations
• Change in DNA of an organism
• Germ mutation- only affects gametes
(offspring?)
• Somatic mutations- in body cells, do not affect
offspring
• Lethal mutations- cause death usually before
birth
• Some mutations are beneficial
Chromosome Mutations
• Deletion is the loss of a piece of chromosome
• Inversion is when a piece breaks off and
reattaches backwards
• Translocation is when a breaks off and
reattaches to another nonhomologous
chromosome
• Nondisjunction is when the chromosome
doesn’t separate and the gamete gets an extra
Gene Mutations
• Point mutation-substitution, addition, or
removal of a nucleotide
– Substitution- one nucleotide is replaced with
another and makes a new codon
• Sickle cell anemia- adenine is substituted for thymine
– Insertion is when a nucleotide is added and
deletion is when one is lost
• Both are serious and cause frame shift mutation (all
codons moved)
Human
Genetics
Chapter 12-2
Studying Human Inheritance
• Study phenotype of members of the same
family and make a pedigree
• Carriers do not express allele but can pass it
on to offspring (recessive)
Genetic Traits and Disorders
• Genetic disorders are diseases or debilitating
conditions that have genetic basis
Traits Controlled by a Single Allele
• Huntington’s Disease is dominant
– Most people find out in their 30s or 40s (after
kids)
– Discovered genetic marker
• Others are controlled by homozygous
recessive
– Cystic fibrosis and sickle-cell anemia
Traits Controlled by Multiple Alleles
• 3 or more alleles of the same gene for a single
trait
– ABO blood type (IA, IB, i)
Blood Typing
Polygenic Traits
• Controlled by 2 or more genes
• Show many degrees of variation
• Also influenced by environment (ex: height)
X-Linked Traits
• Found on the X chromosome
• Colorblindness, Hemophilia, Duchenne
muscular dystrophy
• Not all are diseases, mostly proteins
Sex-Influenced Traits
• The presence of male or female sex hormones
influence traits
• Ex: male pattern baldness
– Both male and female homozygous will lose hair
– Heterozygous males will lose hair, female will not
Disorders Due to Nondisjunction
• Usually causes death
• Monosomy -1, trisomy +1 chromosome
– Down Syndrome (trisomy-21)
– Klinefelter’s Syndrome (XXY)- feminine
characteristics, mental retardation, infertile
– Turner’s Syndrome (X)- female but does not
mature, infertile
• Just Y does not survive
Detecting Human Genetic Disorders
• Genetic screening uses karyotype or blood
tests (+ or – proteins)
• Genetic counseling is medical guidance
• Test Fetus
– Amniocentesis
– Chorionic Villi Sampling
• Or Child (after birth)
– Test for phenylketonuria (PKU) which prevents
the digestion of phenylananine. Can cause brain
damage