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Patterns of inheritance:

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Title: Patterns of inheritance:


1
Patterns of inheritance
Mendel and beyond
2
(No Transcript)
3
Contrasting characters in peas
4
Experiment with garden peas I
5
In this case a true-breeding tall plant was
crossed with a true-breeding short plant. All
of the plants in the next generation were tall.
6
These are the results Mendel obtained when he
crossed two heterozygotes.
7
Paint-pot theory of inheritance
8
Mendels finding was contrary to the prediction
of the Paint-pot theory of inheritance
9
Mendels 1st law-law of segregation
10
Mendels law of segregation -explanation of
monohybrid ratio

11
Mendel described patterns of inheritance in the
1860s, but it wasnt until the early 1900s that
inherited traits, genes, were linked to cellular
structures called chromosomes. The number of
chromosomes varies among species, but all
chromosomes contain genes arranged linearly at
specific locations, called loci.
12
This is how geneticists today represent the cross
from the previous screen. The original plants are
the P generation and their offspring are the F1
generation. The T and t symbols represent
dominant and recessive alleles of a single gene.
13
we breed the offspring to one another in the
cross Tt x Tt, and wish to predict the results
we need to follow the production of gametes
during meiosis. These individuals make gametes
with either T or t in equal numbers.
14
The chance of gametes of different types
encountering one another is represented on a
Punnett square. The genotypic ratio of
homozygous dominant heterozygous homozygous
recessive individuals is 121.
15
Many genetics problems will fall in the category
of a monohybrid cross. They all can be approached
using the model above
16
Testcross. a heterozygote was crossed with a
homozygous recessive individual. A situation in
which an individual of dominant phenotype, but of
unknown genotype, is crossed with one or more
recessive individuals. This can provide
information on the unknown genotype.
17
Dihybrid cross
18
Dihybrid cross
19
Dihybrid cross
The inheritance of two contrasting characters
were considered at the same time
20
Law of independent assortment
21
Mendels 2nd law
22
Mendels 2nd lawexplained byobserving movement
of chromosomes at meiosis
23
Cell division
24
The cell cycle
25
Interphase
26
Interphase
27
Mitosis division of the nucleus
28
Prophasemetaphaseanaphasetelophase
Division of the nucleus
29
Division of the cytoplasm
30
Produce identical daughter cells
31
Mitosis and cell cycle
32
Meiosis
  • Reduction division
  • Generate variability in gametes

33
Meiosis-Interphase
34
Meiosis-prophase I
35
Meiosis-metaphase I
36
Meiosis-anaphase I
37
Meiosis-telophase I
38
Meiosis I -animated
39
Meiosis II
prophase II
metaphase II
anaphase II
telophase II
40
Meiosis II -animated
41
Meiosis-overall
42
Independent assortment
43
Crossing over
44
Anaphase I and IInote new gene combinations as
a result of crossing over
45
Comparing Mitosis and Meiosis
46
Comparing Mitosis and Meiosis
47
Incomplete dominance
In some cases, alleles may not interact in a
dominant/recessive pattern. Heterozygotes have an
intermediate phenotype or express both alleles.
The genotypic ratio will match the phenotypic
ratio. Snapdragons demonstrate incomplete
dominance.
48
Incomplete dominance II
49
Multiple allele
50
Linkage and crossing-over
51
Recombinant frequency
52
Skin colour_a pair of twin sisters
53
Continuous or discontinuous
54
Polygenic effects on genetic variation
55
Polygenic inheritance_skin colour
56
Skin colour is a continuous variation because
57
How would U explain the very different skin
colour of the twin sisters?
58
X-inactivation
59
X-inactivation
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