- Animal development is defined as the progressive changes in size, shape, and function that occur during an organism's life through which its genetic potential is translated into mature systems. - Maternal genes play a major role in early development by providing nutritive and determinative materials to the egg during oogenesis, organizing the egg for subsequent development. Mutations in these maternal effect genes can impact offspring viability without affecting the mother. - After fertilization, zygotic gene expression begins from the embryo genome, directing cell differentiation and organ formation under genetic control. Homeotic genes determine body segmentation by transforming one segment into another.

2. HAFIZ M WASEEM UNIVERSITY OF
EDUCATION LAHORE

3. Genetic control of animal development

4. Contents
 Animal development
 Maternal gene activity in development
 Genetic analysis of development in vertebrates

5. Animal development
 development can be defined as the series of progressive non repetitive changes
that occur during the life history of organisms.
 Or the progressive changes in size, shape, and function during the life of an
organisms by which its genetic potential are translated into functioning mature
systems.

6. Maternal gene activity in animal development
 Materials transported into the egg during oogenesis play a major role in embryonic
development.
 Important events occur in animal development even before an egg is fertilized.
 At this time, nutritive and determinative materials are transported into the egg from
surrounding cells, laying up food stores and organizing the egg for its subsequent
development.
 These materials are generated by the expression of genes in the female
reproductive system, some being expressed in somatic reproductive tissues and
others only in germline tissues.

7. Maternal effect gene
 Mutations in genes that contribute to the formation of healthy eggs may have no
effect on the viability or appearance of the female making those eggs.
 Instead, their effects may be seen only in the next generation.
 Such mutations are called maternal-effect mutations
 because the mutant phenotype in the offspring is caused by a mutant genotype in
its mother.
 Genes identified by such mutations are called maternal-effect genes

8. Maternal effect gene
 Matings between flies homozygous for recessive
mutations in this gene produce inviable progeny.
This lethal effect is strictly maternal.
 A cross between homozygous mutant females
and homozygous wild-type males produces inviable
progeny, but the reciprocal cross produces viable progeny.
 The lethal effect of the dorsal mutation is therefore
manifested only if females are homozygous for it.
The male genotype is irrelevant

9. Zygotic gene activity in development
 The differentiation of cell types and the formation of organs depend on genes
being activated in particular spatial and temporal patterns.
 However, at some point, the genes in the embryo are selectively activated, and
new materials are made.
 This process is referred to as zygotic gene expression.
 The earliest event in animal development are controlled by maternally synthesized
factor .
 After fertilization, zygotic gene expression or expression of genes from the embryo
genome begin.

10. Body segmentation
 In many invertebrates the body consists of an array
of adjoining units called segments
 An adult Drosophila, for example, has a head,
three distinct thoracic segments, and eight
abdominal segments.
Within the thorax and abdomen, each segment
can be identified by coloration

11. Homeotic gene
 Interest in the genetic control of segmentation began with the discovery of
mutations that transform one segment into another.
 So homeotic mutation transform one segment to another this is called homeosis .
 Mutation in bithorax affect two thoracic segments. creating a fly with a small pair of
rudimentary wings in place of the small balancing structures called halters
 Mutation in antennapedia transform
antennae into legs.

12. Organ formation
 Organ formation require the organization of many different type of cell.
 Organ formation is under genetic control.
 The heart, stomach, kidney, liver, and eye are all examples of organs.
The eyless gene
 Mutant flies lack eyeless
 The wild type eyeless gene encode a homeodomain transcription factor that
activate pathway involving thousand of gene.

13. Mamalian homologus of eyeless
 The mouse homologue of eyeless pax6 produce extra eye whwn inserted into
drosophila .
 In mice, mutation in eyeless homologue reduce the size of an eye.
 Mutation in human homologue cause aniridia .

14. Genetic analysis of development in
vertebrates
 Geneticists can study development in vertebrates by applying knowledge gained
from the study of model invertebrates, by
 analyzing mutations in model vertebrates such as mice, and by examining the
differentiation of stem cells.
 One of the most dramatic applications of this approach has shown that vertebrates
contain homologues of the homeotic genes of Drosophila. These so-called Hox
genes
 Many vertebrate genes—for example, the Hox genes—have been identified by
homology with genes isolated from model organisms such as Drosophila and C.
elegans.

15. Hox gene
Among vertebrates, the mouse provides opportunities to study mutations that affect
development.
 Mammalian stem cells, especially those derived from embryos, can be cultured in
vitro to study the mechanisms that underlie differentiation.
 Animals produced by reproductive cloning suggest that differentiated cells have
the same genetic potential as the zygote.
 Recombination between gene segments during immune cell differentiation creates
the sequences that encode the light and heavy chains of antibodies.