Criss cross inheritance

brief about the criss-cross inheritance of traits

2. CRISS-CROSS INHERITANCE:
•It is the transmission of a gene from mother to son or father to
daughter.
•Those patterns of inheritance are called crisscross inheritance or skip
generation inheritance, in which a character is inherited to the second
generation through the carrier of first generation.
•The sex linked characters exhibit criss-cross inheritance

3. Genes on one or other of the sex chromosomes produce
inheritance pattern different from that shown by autosomes:
AutosomAl genes
•All individuals carry two allels of each
genes.
•Dominance operates in both males and
females.
•Reciprocal crosses produce the same
results.
•Alleles passed equally to male and
female offsprings.
sex-linked genes
•Males carry only one alleles of each
gene (hemizygous).
•Dominance operates in females only
•Reciprocal crosses produce different
results.
•‘criss cross’ inheritance pattern: father
to daughter to grandson, etc.

4. RECEPROCAL CROSS:
•It involves a pair of
crosses in which the
phenotypes of the
partners are
reversed.
•Different results
from the two crosses
indicates that sex
linkage of the gene is
controlling the trait.

5. CRISS-CROSS INHERITANCE:
Sex-linked characters, which are controlled by genes on sex
chromosomes are divided into two categories:
•Sex-influenced traits
•Sex-limited traits

6. Sex-influenced traits:
•These are phenotypes affected by whether they appear in a male or
female body.
•Even in a homozygous female the condition may not be expressed fully.
•Example: baldness in humans.
Sex-limited traits:
•These are characters only expressed in one sex.
•They may be caused by genes on either autosomal or sex chromosomes.
•Examples: female sterility in Drosophila

7. Sex linkage & criss-cross inheritance
•Sex-linkage was first discovered by Thomas H. Morgan (father of
modern genetics), (1910) in Drosophila melanogaster.
•When the white-eyed male is crossed to a normal red-eyed female, in
the first generation all the males and females were red-eyed.
•First generation red-eyed female was crossed to a red-eyed male, in
the second generation all the females were red-eyed and 50% males
were white-eyed.
•The white-eyed character from the initial male parent is inherited to
the male of the 2nd generation through carrier female.

8. Sex linkage & criss-cross inheritance
•In a reciprocal cross that involved a second cross of same traits but
carried by sexes reversed, the results were different.
•When a white-eyed female was crossed to a red-eyed male, in the first
generation all the females were red-eyed and males were white-eyed.
•The difference was due to the inheritance of a recessive gene located
on the X chromosome.
•Males always get the sex-linked recessive characters from females due
to a single recessive allele on X-chromosome.

9. CRISS-CROSS INHERITANCE:
•Genes on X but not on Y – leads to a “criss-cross” pattern of
inheritance where sons receive their X chromosome from the
maternal parent and daughters receive an X from both parents
•There are several, well-known sex-linked traits in humans: examples
include hemophilia, color blindness, and the fragile X syndrome
•Holandric inheritance: Genes on the Y but not the X

10. Sex linked recessive inheritance:
For a recessive trait controlled by a gene on the X chromosome, the
features of inheritance are:
•More males than females show the trait.
•A male with the trait cannot pass the allele to sons.
•Carrier females do not show the trait but pass it to sons.
•All daughters of affected males will at least be carriers of the trait.
Sex linked dominant inheritance:
•This is rarer since all the daughters of affected males will be affected
(the heterozygous condition is not a carrier)

11. X- linked dominant inheritance:
X-linked dominant
inheritance works
differently depending
upon whether the
mother (left image)
or father (right
image) is the carrier
of a gene that causes a
disease or disorder.

12. X- linked recessive inheritance:
In X- linked recessive
inheritance mainly the
male offsprings are
affected due to
presence of single X
chromosome.

13. EXAMPLE OF CRISS-CROSS INHERITANCE
- Haemophilia
Transmission of a
character from 1
st

generation male to 3
rd

generation male
including a 2
nd

generation female
shows the criss-cross
inheritance.

14. EXAMPLE OF CRISS-CROSS INHERITANCE
- Colour blindness

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